There is provided an unlocking device, including: a rotating member; a housing; an operating member; and a biasing member. The rotating member includes a pressed portion, and a retaining portion. The housing includes an accommodating portion, an engaging portion that is engaged with the retaining portion, and an opening. The operating member includes a pressing portion, and is slidable in a direction substantially parallel to a rotation plane of the rotating member. The retaining portion and the engaging portion are located within a thickness range of the operating member when viewed in a sliding direction of the operating member.