PURPOSE: To speedily and accurately align optical axes even at the time of long-interval installation by adjusting the optical axes of the projector and photodetector of the infrared-ray type crime preventive warning device by a transmission unit and a reception unit for optical axis adjustment.

CONSTITUTION: The transmission unit 3A is connected to the photodetection part 2A and reception part 4a for optical axis adjustment, an infrared-ray beam is projected from the projection 1, and the optical axes of the projector 1a and photodetector 2a are visually adjusted and aligned with each other, so that signal intensity corresponding to the degree of alignment between the optical axes is obtained. This signal intensity is displayed on a photodetection- side level meter 3b and further on a projection-side level meter 4b through the signal reception part 4a for optical axis adjustment. The optical axes are finely adjusted watching the displays so that the display indicates a maximum value. Consequently, the optical axes can easily, speedily, and accurately be adjusted. After the adjustment, the parts 2A, 3A, and 4A are disconnected and the adjustment is completed.