Zhou Xijun, 48, surrendered about 5 p.m. Tuesday, Xinhua, the official government news agency, reported. The Public Security Department in Jilin province in northeastern China announced the arrest and Zhou's alleged confession on the Chinese equivalent of Twitter.
Police said the baby's body was still missing.
The car, a Toyota RAV 4, was stolen Monday evening from a supermarket owner in Changchun, the provincial capital, police said. The owner said he drove to the store and left his car with the engine running and the baby inside while he made a quick stop to turn on a stove.
The baby's family pleaded on local traffic broadcasts for the return of the child, saying they would not prosecute for car theft.
The car was found abandoned in Gongzhulung City with the baby's clothes and the license plate nearby.