One end portion of a connecting member 31 is connected to a first housing 1 such that the connecting member 31 is rotatable about a first rotation axis L1. The other end portion of the connecting member 31 is connected to a second housing 2 such that the connecting member 31 is rotatable about a second rotation axis L2 parallel to the first rotation axis L1. The first and the second housings 1, 2 are arranged such that when the second housing 2 is rotated up to a predetermined intermediate position, opposite end portions of the first housing 1 in a direction perpendicular to the first and the second rotation axes L1, L2 are protruded from the second housing 2 in the said direction.