A connection device capable of pivotally connecting two housings without a connecting section projecting from the housings, and capable of stably holding the housings when the housings are in an openstate. A connection device has a first and a third connection member (31, 33) that have flexibility and foldably fix an upper housing (1) and a lower housing (2) with a connection section in between.The connection device further has a second connection member (32) that has a restoring force and rigidity returning from a folded state to an open state and has a cross-section with a circular-arc shape curved and recessed toward the folding direction of the upper and lower housings (1, 2).