A muscle activity measurement device comprising: a magnetic sensor unit configured to detect a magnetic field generated from a body; a container; identification means configured to identify a placement direction of the muscle activity measurement device, and which identification means includes identification information configured to be used for placing the muscle activity measurement device such that a sensing direction of the magnetic sensor unit is substantially orthogonal to an extension direction of muscle fibers in the body to be detected or the identification means including identification information configured to be used for placing the muscle activity measurement device such that a sensing direction of the magnetic sensor unit substantially coincides with a direction of a muscular magnetic field generated due to muscle activity in the body to be detected, a calculation unit configured to generate biomagnetic information on the basis of a signal detected by the magnetic sensor unit; a wireless module configured to wirelessly transmit the biomagnetic information generated by the calculation unit to an external device; and a power supply unit configured to supply electric power to the magnetic sensor unit, the calculation unit and the wireless module, wherein the identification information being a display of the placement direction of the muscle activity measurement device on the front surface of the container, or a shape of the container, the container comprises a container body that comprises a substrate having a front surface and a rear surface, which substrate is made of material configured to block environmental magnetism, and has an opening on a front surface side of the substrate, and a lid plate that covers the opening of the container body and has an inner surface facing the front surface of the substrate and an outer surface, the magnetic sensor unit is provided on the rear surface of the substrate of the container, the identification means is provided on the outer surface of the lid plate of the container, and the calculation unit and the wireless module are mounted to the front surface of the substrate. a magnetic sensor unit configured to detect a magnetic field generated from a body; a container; identification means configured to identify a placement direction of the muscle activity measurement device, and which identification means includes identification information configured to be used for placing the muscle activity measurement device such that a sensing direction of the magnetic sensor unit is substantially orthogonal to an extension direction of muscle fibers in the body to be detected or the identification means including identification information configured to be used for placing the muscle activity measurement device such that a sensing direction of the magnetic sensor unit substantially coincides with a direction of a muscular magnetic field generated due to muscle activity in the body to be detected, a calculation unit configured to generate biomagnetic information on the basis of a signal detected by the magnetic sensor unit; a wireless module configured to wirelessly transmit the biomagnetic information generated by the calculation unit to an external device; and the identification information being a display of the placement direction of the muscle activity measurement device on the front surface of the container, or a shape of the container, the container comprises a container body that comprises a substrate having a front surface and a rear surface, which substrate is made of material configured to block environmental magnetism, and has an opening on a front surface side of the substrate, and a lid plate that covers the opening of the container body and has an inner surface facing the front surface of the substrate and an outer surface, the magnetic sensor unit is provided on the rear surface of the substrate of the container, the identification means is provided on the outer surface of the lid plate of the container, and the calculation unit and the wireless module are mounted to the front surface of the substrate.