To provide a trouble detector for an air conditioner capable of detecting any trouble without complicating the construction of a compressor itself.

There are provided on an evaporator 7 a temperature sensor 10 for measuring surface temperature, and a memory 15 for storing a reference temperature of the evaporator 7 and a reference difference temperature between the reference temperature and temperature of the evaporator 7. In a CPU 14, a difference between a calculated reference temperature and a measured temperature is compared with a reference cooling temperature. As a result of the comparison, when the difference between the measured temperature of the temperature sensor 10 and the reference temperature does not reach the reference difference temperature, a judgement that the compressor 20 is in a trouble is made.