To provide a coolant circuit capable of controlling the density and flow of a coolant flowing into an expander without influencing operation of the coolant circuit.

A piping 21 and a piping 22 is passed through an intercoolant heat exchanger 8, the piping 21 is covered by an inflow side clad pipe 23, the piping 22 is covered by an outflow side clad pipe 24, the inflow side clad pipe 23 and the outflow side clad pipe 24 are connected by a first connection pipe 25 provided with a pump 27 and a second connection pipe 26, and a secondary coolant is circulated therein. A delivery amount of the pump 27 is adjusted by detected values of a first temperature sensor 30 and a second temperature sensor 31 to change a circulation amount of the secondary coolant.