To provide a motion tracker device that can calculate an angle of an object to a camera coordinate system with high accuracy.

A motion tracker device 1 provided with an actual measurement position calculation part 24 calculating respective actual measurement positions of each optical marker 7 to a camera coordinate system, a storage part 42 for storing reference information indicative of respective reference positions of each optical marker 7 to the camera coordinate system and an angle calculation part 27 comprises: a true position calculation part 25 that calculates respective true positions of each optical marker 7 at time t_(n-1) on the basis of an angular velocity from the time t_(n-1) to time t_n and an actual measurement position at the time t_n; and an update part 26 that updates the reference information, using the true position at the time t_(n-1). The angle calculation part 27 calculates an angle of an object 10 to a reference coordinate system at time t_(n+1) on the basis of an actual measurement position at the time t_(n+1) and the updated reference information.