A lock device has: a cylindrical case member in which is formed a space extending in an axial direction; a cylindrical sleeve member is disposed at an interior of the case member, and is supported and configured to move along the axial direction between a predetermined standby position and an operating position; a plunger member which is disposed at an interior of the sleeve member and configured to move along the axial direction, and which is supported and configured to move between the standby position and the operating position, and in which a key insertion hole, which is for insertion of a key from an outer side at the standby position, is formed along the axial direction; a plurality of tumbler members disposed at the plunger member and configured to move along a direction orthogonal to the axial direction between proper positions, a side lock member disposed at the plunger member and configured to approach and move away from the tumbler members, and an interlocking mechanism which, at a time when the connection of the plunger member and the sleeve member is cancelled by the side lock member, when the plunger member becomes integral with a proper key and moves to the operating position, transfers pushing force from the plunger member to a mechanism to be operated.