An external mechanism for an endoscope includes: a bending wheel configured to engage with a second UD knob of a second bending operation device provided in an operation portion of an endoscope; a motor portion configured to generate a driving force for rotating the bending wheel; a housing case housing the bending wheel and the motor portion and detachably attached to the operation portion, and an operation switch arranged outside the housing case and configured to output a control signal to the motor portion due to the operating element being operated, in which the operation switch is pivotally supported by the rotation shaft and rotates with respect to the housing case.