An operation support device includes a manipulation input unit and an operating section to which a surgical instrument is attached and which operates the surgical instrument. The surgical instrument includes a treatment section, a flexible insertion section, and a manipulation section which is fixed to the flexible insertion section. The manipulation input unit further includes a detection body which is attached to the manipulation section, and a detecting device which detects the detection body. The detecting device calculates information which is capable of specifying a position and/or an orientation of the detection body. On the basis of the information which is calculated by the detecting device, a control device controls an operation of the surgical instrument by outputting to the operating section an order of moving the surgical instrument as a manipulation order.