Yasuhide Mizobata fled into an apartment building yesterday afternoon after firing repeatedly at officers who challenged him, a force spokesman said.
About 17 hours later the suspect shot himself in the abdomen, public broadcaster NHK and Jiji Press reported.
NHK footage showed police storming the building after hearing a gunshot as an ambulance apparently carrying the suspect sped off. The broadcaster said police arrested him.
He was then treated in hospital but later confirmed dead, NHK said.
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The standoff surprised Japan, where gun violence is exceedingly unusual and there are very strict controls on firearms ownership.
Mizobata had spent the night holed up in the building, surrounded by heavily-armed police trying to persuade him to surrender.
Television footage had showed him brandishing two pistols as he stood atop scaffolding.
Media reports said the suspect had threatened to shoot police and turn the gun on himself during the overnight standoff in Wakayama, 450 kilometres southwest of Tokyo.
Broadcasters said the building was been evacuated as the incident began. Local residents were told to stay indoors.
He is reportedly the son of the company owner.
Mizobata had been scheduled to go to jail on Monday after having been convicted of drugs charges, the Sankei Shimbun daily said.
In 2015 Japan had just eight reported gun crimes nationwide, with one person killed and three wounded.
The few weapons in circulation are often linked to organised crime.
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