To provide an on-vehicle air-conditioner which is mounted on a vehicle having a constant-temperature chamber to perform cold storage or heated storage of an article therein, and capable of cooling or heating the inside of a cabin C even when the vehicle is stopped for a long time while a vehicular engine EG is stopped.

The on-vehicle air-conditioner comprises an in-chamber heat exchanger 31 to exchange heat between the air in a constant-temperature chamber 100 and a heating medium, an in-cabin heat exchanger 32 provided in a cabin C, a heating medium circulating passage 36 formed between the heat exchangers 31, 32, a water pump 33 provided in the heating medium circulating passage 36 to circulate the heating medium, and a blower 34 to blow the air heat-exchanged with the heating medium into the cabin C by circulating the air in the in-cabin heat exchanger 32.