A clamping device comprising: a one end portion having a first projection on an inner side and a locked part at a tip; an other end portion having a second projection at a position facing the first projection, a locking part capable of locking the locked part; a middle portion continuous with the one end portion and with the other end portion; and a first insertion hole allowing a flexible tube to be inserted between the first projection and the second projection, wherein a clamped state where the locked part is locked by the locking part is established when the one end portion is pressed and is brought closer to the other end portion, and an unclamped state is established when the locked part locked by the locking part is unlocked by bending the other end portion such that the other end portion is displaced from the one end portion, the clamping device being configured to clamp the flexible tube in the clamped state where the first projection and the second projection are positioned close to each other to intercept a flow of a fluid at a clamped position, wherein the clamping device further includes a displacement-restricting member capable of restricting the displacement of the other end portion in a transition from the clamped state to the unclamped state, wherein the other end portion further comprises a part extending substantially linearly from the middle portion and a part standing therefrom while being bent wherein the middle portion has the first insertion hole and the part standing from the other end portion has a second insertion hole, and the flexible tube is to be inserted into the first insertion hole and the second insertion hole the clamping device comprises wall portions and a part of the displacement-restricting member is formed on the wall portions wherein the wall portions are integrally formed on the other end portion at two respective side edges of the other end portion. a one end portion having a first projection on an inner side and a locked part at a tip; an other end portion having a second projection at a position facing the first projection, a locking part capable of locking the locked part; a middle portion continuous with the one end portion and with the other end portion; and a first insertion hole allowing a flexible tube to be inserted between the first projection and the second projection, wherein a clamped state where the locked part is locked by the locking part is established when the one end portion is pressed and is brought closer to the other end portion, and an unclamped state is established when the locked part locked by the locking part is unlocked by bending the other end portion such that the other end portion is displaced from the one end portion, the clamping device being configured to clamp the flexible tube in the clamped state where the first projection and the second projection are positioned close to each other to intercept a flow of a fluid at a clamped position, wherein the clamping device further includes a displacement-restricting member capable of restricting the displacement of the other end portion in a transition from the clamped state to the unclamped state, wherein the other end portion further comprises a part extending substantially linearly from the middle portion and a part standing therefrom while being bent wherein the middle portion has the first insertion hole and the part standing from the other end portion has a second insertion hole, and the flexible tube is to be inserted into the first insertion hole and the second insertion hole the clamping device comprises wall portions and a part of the displacement-restricting member is formed on the wall portions wherein the wall portions are integrally formed on the other end portion at two respective side edges of the other end portion.