To provide a thermostat capable of contactless detection of temperatures having high thermoresponsive properties, and also having waterproof property and dust proof property.

A stationary contact 2 is fixed to the base 1. As for a leaf spring4, the base end is retained by the base 1, a movable contact 3 is installed at the tip part, and the movable contact 3 is biased upward so as to be contacted with the stationary contact 2. A guide pin 5 is vertically movably arranged at the upper part of the leaf spring 4, and the movable contact 3 is made to be separated from the stationary contact 2 by pressing the leaf spring 4 down based on the reversing operation of a bimetal 6. At a cap 16 installed so as to cover the bimetal 6, an opening 16d is installed. This opening 16d is closed by an infrared ray transmissible material such as glass.