An infrared sensor includes a MOSFET sensor, and a current source MOSFET which is connected to the MOSFET sensor in series and constitutes a constant current source for driving the MOSFET sensor with a constant current, wherein a terminal between the MOSFET sensor and the current source MOSFET constitutes a sensor output terminal, the MOSFET sensor is disposed on a heat-insulated structure, the current source MOSFET is disposed outside the heat-insulated structure, and the MOSFET sensor and the current source MOSFET are constituted by a same conductivity type MOSFET and operate in a subthreshold region.