The protesters are calling on Prime Minister Shinzo Abe to drop the bills which would clear the way for the country’s first combat since the Second World War.
Many constitutional experts believe the bills contravene the country’s war-renouncing constitution.
Organisers estimate about 120,000 people have taken part in the rally in Tokyo’s government district against the bills.
Japan’s lower house has already passed the controversial legislation, and the upper chamber is expected to endorse it.
Under its constitution, Japan is prevented from using force to resolve conflicts, except as a means of self-defence.
The reinterpretation of the law would allow what is being referred to as “collective self-defence” — using force to defend allied nations under attack.
This protester in Tokyo says the proposed bills contradict the intention of Japan’s pacifist constitution.
“We hope all Japanese are proud of the pacifist constitution. Only after apologising to Asian countries and announcing it will never wage wars can Japan be recognised by the international community. If Japan can’t abide by the constitution, the future will be dim. The Abe regime ignores the public opinions, just like Hitler. We cannot tolerate this regime any longer.”
The leader of the opposition Democratic Party of Japan, Katsuya Okada, says a united response from the country is needed to strike down the bills.
“We need your help, and let’s unite in the next three weeks in making sure to scrap the bill.”
The leader of the opposition People’s Life Party, Ichiro Ozawa, told the crowd his party strongly opposes the legislative changes.
“No matter what, we will join hands to stop this ridiculous, stupid and dangerous law from passing, and let us bring down the Abe administration.”
More than 300 rallies were staged across Japan over the weekend in opposition to the government’s proposed bills.
The Tokyo demonstration was the biggest in the capital since mass protests against nuclear power in 2012 after the March 2011 Fukushima atomic disaster.
This protester says the changes simply go against the country’s pacifist tradition.
“We oppose solving problems through war. We believe real peace will be realised through dialogue and negotiation.”