An underwater mask includes a buckle with a strap that can be moved and adjusted in the up-down and lateral directions on a wearers head. The buckle includes a base including a spring with a locking hook, a strap adjuster body turnably attached to the base and including a plurality of engaging teeth configured to sequentially engage with the locking hook according to the turn, a handling member held inside the body and operated from outside the body, and a stopper held by the body. The handling member includes a spring, sliding portion, and a pair of finger pads exposed outside the body by the spring. The stopper includes a sliding contact tapered protrusion that slides sliding against the pair of sliding portions to cause the stopper to swing toward a direction opposite to the strap adjuster body and release the pawl from the engaging teeth of the strap.
