To positively protect a driving means in a heat exchanger circuit without causing a malfunction due to a chattering phenomenon or the like and without causing an increase in costs.

A moving contact 35 is movably provided between a driving contact 37 connected to the driving means of the compressor and a holding contact 38 connected to an electromagnet 42. A power source is connected to the moving contact 35 via an air conditioner switch 41. A bellows member 34 is provided having a bellows part 33 fluctuated by pressure LP of a low pressure side. A moving contact frame 36 with one end fixed to the moving contact 35 is fixed to the bellows part 33. When the pressure of the low pressure side becomes a predetermined value or less, the moving contact frame 36 is moved by the bellows part 33, the moving contact 35 is moved toward the holding contact 38 side and brought into contact with it, electric power is fed to the electromagnet 42, the moving contact frame 36 is magnetically attracted to the electromagnet 42, and the moving contact 35 is separated from the driving contact 37 until the air conditioner switch 41 is turned off.