An infrared imaging device, including: connection wiring portions arranged in matrix form on a substrate which is mounted in a package; first and second infrared detecting portions configured to convert intensity of absorbed infrared radiation into respective first and second signals, the second infrared detecting portion being smaller in thermal conductance than the first infrared detecting portion; and a lid member attached to the package so as to define an air-tight gap with the substrate, the connection wiring portions, the first and second infrared detecting portions being accommodated within the gap; wherein a degree-of-vacuum is measured within the gap and a warning issued based on the measured degree-of-vacuum.