To provide a motion converting device capable of freely setting and varying the axial direction of the rotary motion or the direction of a rectilinear motion after the conversion of motion in the axial direction of the rotary motion before the conversion.

This motion converting device 1 includes a first bevel gear 4 fixed to a first rotary member 3, a third bevel gear 6 provided to rotate on a second axis β intersecting perpendicularly to a first axis α and always meshing with the first bevel gear 4 from above, a second rotary member 9 capable of rotating on a third axis γ intersecting perpendicularly to the second axis β, a fifth bevel gear 10 provided to rotate integrally with the second rotary member 9 and always meshing with the third bevel gear 6, a cylindrical female screw member 12 provided to rotate integrally with the second rotary member 9, and a screw shaft rod 13 in the third axis γ direction screw-engaged with the female screw member 12. The axial direction of the third axis γ is free to the axial direction of the first axis α. The rotary motion of the first rotary member 3 is converted to the rectilinear motion of the screw shaft rod 13 in an arbitrary direction.