A wrist-worn input device measuring a biopotential for use in gesture inputting, includes a band that forms at least part of a tubular structure having a first opening and a second opening at the two ends thereof in an axial direction thereof, an electrode open to an internal surface of the band, a position determination unit disposed close to the first opening and having a shape to be engaged with at least part of a periphery of the styloid process of ulna of a user, a biopotential measurement unit that measures the biopotential of the user using the electrode, and a measured potential transmitter that outputs the biopotential of the user.