A first coupling member 20 can be engaged with a first engagement hole 2e and held slidably by a first support member 12. A second coupling member 30 of the present embodiment can be engaged with a second engagement hole 2f and held slidably by a second support member 13. With this configuration, a relative position between a second housing 2 and a protection cover 10 changes at the time of turning the second housing 2 in a direction indicated by an arrow A or B, which can prevent the protection cover 10 from loosening significantly near the hinge portions 3.