An apparatus and method for evaluating the degree of work comfort of a user is disclosed. A pair of sensors detect myoelectric potentials of a pair of bilaterally symmetrical muscles. A waveform processing unit generates a synchronous contraction waveform by either using the smaller value between signals from the two muscles at a given time, or by determining the geometric mean between the signals at a given time. An evaluation unit uses the intensity or frequency information from the synchronous contraction waveform to evaluate the user's level of comfort performing a task such as driving.