Abstract: A wrist band for a device main body containing communication circuits, having a first wrist band at least partially covering a first antenna plate, a second wrist band at least partially covering a second antenna plate, and a clasp device including a contact mechanism for electrically connecting the first antenna plate and the second antenna plate to form a loop-like antenna when the second wrist band and first wrist band are clasped. The clasp device is releasable and has a three-fold stricture. The clasp device includes a clasp lower plate having a base end portion fixed to the first wrist band, a clasp intermediate plate connected to the clasp lower plate, a clasp upper box connected to the clasp intermediate plate and fixed to the second wrist band and a clasping lock mechanism that fixes the clasp upper box to the clasp lower plate when the clasp intermediate plate is rotated and overlapped onto the clasped lower plate.