To solve the problem of a thermopile sensor infrared detector, wherein since the number of mounted members is small and heat capacity is small for the volume in the thermopile type infrared detector, thermal effects to a thermopile chip are large, when a rapid environmental temperature change is given, resulting in drifting of a signal output in response to the environmental temperature change.

A substrate on which members, such as a resistor, a capacitor and an operational amplifier serving as a circuit section in the thermopile type infrared detector are mounted is stored, to increase an internal member volume and heat capacity.