A lock device has: a case member which is cylindrical shaped and in which is formed a space extending in an axial direction; a sleeve member which is cylindrical shaped, and 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, which correspond to engaged portions of a proper key at which proper engaged portions are provided, and improper positions, which do not correspond to the engaged portions, and engaging concave portions are formed in peripheral edge portions of the tumbler members, and when a proper key is inserted into the key insertion hole of the plunger member, the tumbler members move to the proper positions, and when an improper key is inserted, at least one of the tumbler members is at an improper position; a sidelock member disposed at the plunger member and configured to approach and move away from the tumbler members, and when an improper key is inserted in the key insertion hole, the side lock member moves apart from the engaging concave portions of the tumbler members and connects the plunger member and the sleeve member along the axial direction, and when a proper key is inserted in the key insertion hole, the side lock member engages with the engaging concave portions of all of the tumbler members and cancels connection of the plunger member and the sleeve member.