A muscle training device includes an insulating sheet configured such that electrodes are exposed on an inner surface closely contacting a body surface above a muscle, a stimulation signal output unit configured to output an electrical stimulation signal to a stimulation electrode which is at least any of the electrodes, a myoelectric signal detection unit configured to detect, while output of the electrical stimulation signal is stopped, a muscle action potential shown at a myoelectric detection electrode which is at least any of the electrodes, and a muscle condition determination unit configured to determine the state of action of the muscle from the muscle action potential of the myoelectric detection electrode. The stimulation electrode to which the electrical stimulation signal is output and/or the method for outputting the electrical stimulation signal are/is adjusted according to the state of action of the muscle determined by the muscle condition determination unit.
