Robinson says that the onus is now on the Macedonian authorities to implement change
He said the rebels fighting the government were handing in their weapons, and that the Macedonian parliament now had a moral obligation to fulfil its side of the peace agreement.
Meanwhile the German parliament has voted to allow German soldiers to join the Nato mission in Macedonia - the first German troops are due to leave on Wednesday night.
Nato troops are now into their third day of weapons collection and they hope to have reached a third of their target of 3,300 weapons by the end of Wednesday.
Successful operation
Lord Robertson flew by helicopter to visit a depot at Krivolac in central Macedonia where the turned-in weapons are being held.
Speaking afterwards he said that the operation was going well so far and that even local politicians had been surprised by how successful it had been.
He said the Macedonian parliament now had a "moral obligation" to honour the agreement, and he expected members to vote it through.
"Insurgents are disarming, handing over the weapons and disbanding as well.
"Just as I expect the insurgents to disarm, I expect the members of the Macedonian parliament to recognise their responsibilities," he said.
He warned that the alternative to the Nato plan would be horrifying to all who lived in Macedonia.
"I hope these people of Macedonia will see these weapons coming out of Macedonian politics and will draw the right lessons," he said.
'One third collected'
He again defended Nato's decision to set the target for weapons to be handed over at just over 3,000 - far below the number the government says are in rebel hands.
"Its not just the number of weapons that matter, it is the fact that the so-called NLA is handing over these weapons and disbanding its organisation," he said.
There are reports that Nato troops have already collected one third of the weapons held by ethnic Albanian rebels, fulfilling part of its agreement with the Macedonian government.
Nato had pledged to gather one third by Friday, before parliament meets to debate implementing a wider peace agreement.
Mr Robertson said that he expected General Gunnar Lange, the commander Operation Essential Harvest, to be able to confirm the meeting of that target by Friday.
Mr Robertson also said that he remained confident that Nato would be able to complete its task within its 30-day time period.
Disarmament to continue
Meanwhile Macedonia's hard-line Interior Minister Ljube Boskovski said that government security forces would ensure that the task of disarming the paramilitaries would continue after Nato leaves.
"We have to act repressively to show we are serious as a country and that we intend to disarm all those bandits that can upset the peace in Macedonia," he said.
He said that a special reserve unit, known as "The Lions" was being formed to deal with the aftermath of the Nato withdrawal, but denied that the new force was a paramilitary group too.
"It will be an anti-terrorist unit for rapid intervention... to clear the terrain of remaining bandits," he said.