To provide a mold thermostat capable of improving heat efficiency by decreasing one amount of a medium recovered by switching high/low temperature media.

The mold thermostat 1 includes a high-temperature medium supply part 2, a low-temperature medium supply part 3, a medium-feeding side switching connection part 4 and a medium-returning side switching connection part 5 near a mold 8, a high-temperature medium storage part 20, a low-temperature medium storage part 30, a recovered medium storage part 60, and a pipe line. After a control part changes a mold heating state to a heating/cooling switching state in which a low-temperature medium sending route 14, the pipe line, a recovered medium storage part 60, and the low-temperature medium storage part 30 are communicated/connected, the control part switches the state to a mold cooling state. On the other hand, after the control part changes the mold cooling state to a cooling/heating switching state in which a high-temperature medium sending route 11, the pipe line, a recovered medium storage part 60, and the high-temperature medium storage part 20 are communicated/connected, the control part switches the state to the mold heating state.