PURPOSE: To arrange so that an heating operation may be carried out properly, by controlling a throttle valve to have a proper opening according to the degree of coolant gas overheating at the outlet of a heat exchanger on the user's side at time of cooling operation and the degree of coolant liquid overcooling at the outlet of a heat exchanger on the user's side at time of heating operation.

CONSTITUTION: A throttle valve control device 25 receives as an input signal an output from the first temperature detector 11 for detecting a condensation temperature of a heat exchanger 3 on the user's side and from the second temperature detector 12 for detecting a coolant temperature betweena heat exchanger 3 on the user's side and a throttle valve 13 during heating operation. While during cooling operation, said device receives an output from the first temperature detector 11 for detecting an evaporation temperature of a heat exchanger 3 on the user's side and from the third temperature detector 14 for detecting a coolant temperature between a heat exchanger 3 on the user's side and a four-point valve 2. The opening of a throttle valve 16 is controlled according to these signals received.