A flow channel switching device provided in an oil circuit to switch the oil flow channel in accordance with the temperature of the oil. The flow channel switching device includes: a thermo-valve case that includes a plurality of flow passages that are communicated outside of the case; and a cylinder that is formed to move in the thermo-valve case and switches the oil flow channel in accordance with the temperature of the oil. The cylinder moves to a predetermined position and is fixed by means of an external member when the fluid at a low temperature is fed into the fluid circuit.