To provide a myoelectric sensor of high performance to noises, which is easy in positioning when applied to a human body, easy in maintenance, and simple in manufacturing.

The myoelectric sensor equipped with at least two sensing electrodes to be brought into contact with the living body for measuring myoelectricity from a potential difference between the two sensing electrodes of the many detecting electrodes, which includes a main body case storing a plate at least provided with the sensing electrodes and a myoelectricity detecting means. A fastening means capable of attaching/detaching a supporting body designed to be suitably attached to a subject's body to/from the main body case is respectively provided to the main body case and the supporting part. The main body case, and the fastening means are made of constitution including a conductive material, and at least a side of the supporting part to be brought into contact with the living body are able to obtain a reference electric potential of the living body to be obtained by the constitution including a conductive material. The reference electric potential obtained by the supporting part is conducted to the myoelectricity detecting means through the fastening means and the main body case.