Ushio Sato, 23, was caught red-handed trying to make off with the unmarked police car in his failed pre-dawn heist on Monday, said a police spokeswoman in the central city of Numazu.
She declined to give more details.
Japanese media reports said the luckless Sato did not notice there were officers inside the unlocked vehicle, which was at a local parking lot.
He immediately fled but was quickly caught, according to the Sankei newspaper.
It was not clear if the officers were wearing uniforms or were on duty at the time.