It is an object of the present invention to provide an opening/closing device which can be produced simple in construction and reduce the surface pressure of its cam portions, and a mobile phone which can be reduced in cost and sufficiently reliable in the hinged members by using the opening/closing device. In the opening/closing device operable to rotate the second member (30) with respect to the first member (20) hingedly connected the second member (30) in an opening operation direction by operating first and second rotation cams (160, 140), and a movable cam (150) held in engagement with the second rotation cam (140) in response to the displacement of the operation cam (130), the second rotation cam (140) and the movable cam (150) have a plurality of kinds of end cam portions ((142, 153), (143, 154)) formed thereon at different radiuses (r1, r2) from the guide center axis (110c) in opposing relationship with each other, the urging direction of the urging means (170) to the second member (30) is changed by the end cam portions ((142, 153), (143, 154)) when the operation cam (130) is operated to cause the first rotation cam (160) to be rotated from the predetermined operation starting position.