An operation input device that has multi jointed arms includes: a holding unit that holds proximal ends of the multi-jointed arms in a state in which a relative positional relationship between the proximal ends is fixed a detection unit that detects a joint movement amount that represents a movement of a joint by a rotation angle or a translational displacement from an unknown initial joint value engagement units that are provided in distal ends of the multi jointed arms a data acquisition unit that acquires a plurality of sets of joint movement amounts detected by the detection unit in a time series when engaging and moving the distal ends and an initial value calculation unit that calculates the unknown initial joint value under a condition that a relative positional relationship between the distal ends is fixed via the engagement units.
