To improve portability so as to stably hold the head of a wearing person and have a compact form at the time other than the loading time.

The head-mounting type optical device 1 includes an optical unit 2 disposed in front of wearing person's eyes, a main frame 4 having the optical unit 2 attached thereto, a pair of side frames 5 attached to both ends of the main frame 4 to be folded and disposed in a back-and-forth direction along the side head of the loading user, a pair of slide frames 6 disposed along the side frames 5 to slide and supporting a pressing part 11 pressed to at least the rear head of the loading user, connection parts 10a and 10b for detachably connecting the slide frames 6 to each other, and an energizing member 12 for energizing the slide frames 6 forward with respect to the side frames 5.