An operation mechanism includes: a longitudinal member having a channel a subject operation section provided at a distal end side of the member an operation section provided at a proximal end side of the member a first transmission means connected to the subject operation section at a distal end side thereof and formed to penetrate the operation section transmitting a first driving force a first input portion provided in the operation section and connected to a proximal end side of the first transmission means to operate the subject operation section a second input portion provided closer to the subject operation section side of the operation section than the first input portion and operated by a medical instrument inserted through the channel and second transmission means connected to the first input portion and the second input portion and transmits a second driving force.
