A surgical treatment instrument includes a holdable housing, a shaft, an end effector configured to perform a bending movement with respect to the shaft, a rotor configured to rotate about a rotation axis in response to an operation input performed through an operation member, and a transmission member configured to transmit a driving force for causing the end effector to perform the bending movement to the end effector. The operation member and the transmission member are configured to rotate together with the shaft and the end effector in response to the operation input, and the rotor is configured to not rotate together with the shaft and the end effector when the operation input is performed.
