A portable electronic device 100 includes a horizontally long casing, both ends of which are gripped by a user's both hands, respectively. The device further includes a LCD fit into the front face of the casing 10. Outwardly projecting bulges are respectively formed at both sides of the rear face of the casing where fingers of the user gripping the casing 10 placed. Since the fingers and palms are naturally flexed to fit to the dome-like bulges 42L, 42R, the portable electronic device 100 fits comfortably in the user's hands. The operability is hard to be degraded even if the device is vibrated strongly during a game play with the device.