In the present invention, a ground pattern is formed on a substrate. A pyroelectric element and an electronic circuit element are mounted on the substrate. The electronic circuit element outputs an electrical signal dependent on a voltage generated in the pyroelectric element. The substrate is supported by a stem. The stem includes a lead terminal that outputs the electrical signal from the electronic circuit element, a ground lead terminal that applies a ground potential to the ground pattern from outside, and a support electrically connected to the ground lead terminal. The ground pattern formed on the substrate is electrically connected to the support at least at two positions. The above configuration increases a noise reduction effect.
