a thin timepiece having a module stably fixed therein has a case integrated with a wrist band and a case back , the case having an opening portion on a front surface side thereof , a module having a housing formed of a resin and a timepiece movement held by the housing , the module being removable retained in the opening portion of the case , and a cover glass for covering the opening portion of the case . the housing has at least one two - sided supporting beam integrally formed in a side surface therof and being deformable in a planar direction of the housing , and a fitting projection protruding from each two - side suporting beam , and the module is fixed in the opening portion of the case by inserting the fitting projection into a corresponding engaging recess formed in an inner side face of the case .