"We are looking for balancing factors in the region and Japan could be a significant balancing factor," he told the paper amid growing tensions over the South China Sea, almost all of which is claimed by China.
Foreign department spokesman Raul Hernandez confirmed the government's view that Japan should upgrade its military from a self defence force so that it has more freedom to operate in the region.
"(Del Rosario) said we are in favour of Japan's gaining strength," Hernandez told AFP.
Japan occupied the Philippines for more than three years from December 1941, during which suspected guerrillas were tortured and executed, and some local women forced into prostitution to serve the occupying army.
The war claimed at least a million civilian Philippine lives, according to historians.
The newspaper interview comes shortly before a general election in Japan where the front-runner, opposition leader Shinzo Abe, has said he wants to revise the country's pacifist constitution, imposed by the US after the war.
China claims most of the South China Sea, including waters close to the shores of its neighbours. These areas include major sea lanes and are believed to hold vast mineral and oil resources.
China's claim is contested by the Philippines as well as Brunei, Malaysia, Taiwan and Vietnam, which have overlapping claims to some or all of those same areas.
In April, Chinese patrol vessels prevented the Philippine Navy from arresting a group of Chinese fishermen at the Scarborough Shoal, which is close to the main Philippine island of Luzon and which Manila says is part of its territory.
Manila says China has continued to station patrol vessels in the area even after the Philippines withdrew its vessels and called for a peaceful resolution to the dispute according to international law.
Earlier this month, the Philippines asked China to clarify press reports Chinese authorities had authorised its forces to interdict ships entering what Beijing considers its territorial waters.
China and Japan are also in dispute over islands in the East China Sea that are controlled by Tokyo.