To provide a wrist band attachable/detachable to/from a storage medium and easy in fitting to an arm.

The wrist band comprises a medium storage unit 10 to store an IC storage medium in an attachable/detachable manner, a band portion to be formed of a ring having an arbitrary diameter according to the size of the arm, and a band lock portion to maintain the ring-forming condition, and the medium storage unit, the band portion and the band lock portion are integratedly formed of a same material with each other. A surface of the arm side of the medium storage unit when fitted is opened, and a plurality of projecting portions to temporarily hold the medium projected inward are provided on an inner wall surface of a storage space. The band portion supports a back surface of the IC storage medium when fitted to the arm. The band lock portion comprises an uneven portion 32 comprising a large number of grooves on the surface of the band portion, and a band engagement body 31 having claw-like projection portion to be fitted to the grooves of the uneven portion.