The signal processing board includes a plurality of signal processing circuits configured to process signals output from a plurality of pixels of an infrared detecting element. The signal processing board includes an element placement area where the infrared detecting element is placed, and a circuit placement area positioned outside the element placement area to surround the element placement area when viewed from a direction orthogonal to the signal processing board. The signal processing board includes a plurality of insulating layers that are stacked on a surface side opposing the semiconductor substrate. A plurality of signal processing circuits are placed in the circuit placement area. A heat-conducting layer is placed to be positioned on at least one of the insulating layers and in the element placement area, in the signal processing board. The heat-conducting layer has a heat conductivity that is higher than a heat conductivity of the insulating layers.