The present invention addresses the problem of providing a muscle activity measurement device and a muscle activity measurement method which make it possible to measure the muscle activity of an object to be sensed with increased accuracy. The muscle activity measurement device 1 according to the present invention is provided with a magnetic sensor unit 11 which senses a magnetic field generated from a living body, and an identification means which identifies an installed direction of the muscle activity measurement device 1. The identification means includes an indication 24, on a surface of a container 20, which comprises identification information for installing the muscle activity measurement device 1 in such a way that a magnetism sensing direction X of the magnetic sensor unit 11 and the direction in which the muscle fibers of the living body as the object to be sensed extend are substantially orthogonal to each other.
