To certainly fix a wrist watch on a wrist by partitioning a hollow inside part from a bottom surface part and a bulged part constituted of an elastic material, providing a through hole to introduce air to an upper part of the bulged part and providing an air holding valve between a lower part of the bulged part and the bottom surface part.

A bulged part 1b of an air pump 1 is formed of an elastic material, and a through hole 1a to incorporate air from outside is provided on an upper part of the bulged part 1b of the air pump 1. A thick pressure part 1b1 is formed on a main part and a thin cylindrical part 1b2 is formed on an outer wall part on the bulged part 1b, and connection of the pressure part 1b1 and the cylindrical part 1b2 is formed of a thin groove part 1b3. Air compressed as it is closed with a finger is delivered outside through an air holding valve 2 in the through hole 1a. Thereafter, when the finger is removed, outside air is introduced inside from the through hole 1a, and the air pump 1 returns to its original shape by restoring force of the bulged part 1b. Consequently, it is possible to certainly fix a wrist watch.