To facilitate the mounting of fragile members and to make the process efficient to contribute to make components smaller and low in cost, especially for a pyroelectric infrared ray sensor.

A plurality of elements are arranged closely to each other on a substrate 11 to form an element member array 12, which is temporarily bonded to a jig 13, and then the substrate 11 is removed by etching. Then, it is overlaid to a mounting substrate for joint by half with a single interval longitudinally and laterally, and released from the jig for mounting, which process is repeated for the remaining half later. Since no cut-merging is required on a substrate, the material cost and the number of processes are reduced, and elements are cut diagonally after mounting for separation with least damage to the element. A film-like pyroelectric infrared ray sensor is easily assembled by the process, resulting in smaller size and lower cost.