PURPOSE: To enable to open and close a valve for opening and closing an intake passage of a compressor by the function of a shape memory alloy, by detecting the temperature of intake fluid correctly through provision of a heat-insulating material or a hollow space between the shape memory alloy and the intake passage.

CONSTITUTION: A rear case 13 and a valve case 15, formed at the section incorporating a coil spring 16 made of a shape memory alloy, are kept apart from each other by the intermediary of a hollow space. One end face of the coil spring 16 is supported by a heat-insulating material 22 while the other end face is supported by a spool 17. Here, since the coil spring 16 detects only the temperature of intake cooling medium and causes expansion and contraction with high accuracy, being not influenced by hot discharge gas filled in the rear case 13, a valve in an intake passage 23 can be opened and closed at a proper timing.