A body motion measuring apparatus is described, embodiments of which include an apparatus for detecting the magnitudes of motions in different directions at a time using body motion sensors, calculating the size V of a composite vector based on the relationship between the magnitudes of the motions, comparing the size V of the composite vector with a reference value to determine whether the size V of the composite vector is adequate, calculating an angle θ based on the relationship between the magnitudes of the motions when V is determined to be adequate, calculating a body motion output M taking the angle θ into account, and counting a predetermined body motion based on the relationship between M and a predetermined elapsed time.