To comfortably attach an optical visual device according to the individually varied shapes of heads by providing the device with a head belt adjustment means roughly adjusting the length of a head belt according to the circumference of the head and a buckle type ratchet mechanism finely adjusting the length of the head belt.

The length of the head belts 12A and 12B is roughly adjusted at the central position of the back of the head according to the circumference of the head. That means the rough adjustment corresponding to the circumference of the head is executed by sticking a scotch tape 12c to the proper position of a joined part 12d and peeling and deviating it from the joined part 12d when the adjustment is corrected. Then, the final adjustment is executed by a buckle 13. When the fine adjustment in the tightening direction of the head is executed by the ratchet mechanism of the buckle 13 executing the fine adjustment of the length of the belt according to the circumference of the head, the engagement projection of a switch piece is slid on the surface of the recessed and projecting part of a slide belt 14 while being engaged with it by generating ratchet noise.