To provide a device for measuring body motion for measuring body motions with small errors and at low cost.

A body motion sensor simultaneously detects mutually perpendicular motions of X direction and Y direction as follows: a resultant vector calculating means calculates the amount V of the resultant vector; a resultant vector determining means compares and determines whether the amount V of the resultant vector is ≥ reference value recognized as the output of the body motion; an angle calculating means calculates an angle θ, in terms of tangent with a ratio of mutually perpendicular amount of motions X to Y; a body motion output calculating means calculates a body motion output M which takes into consideration the angle θ; and a body motion counting means counts regarding the prescribed body motion.