The model for the estimation of the amount of mental stress was proposed and the validity of this proposed model was discussed. Emotional sweating rates on solving the mathematical problems which were given as mental stimulation were measured by using the apparatus for continuous recording of emotional sweating rate. The follwing was found out; (a) The normal variation of emotional sweating rates correlate with the subjective difficulty level. (b) The estimated value by this proposed model correlate with the subjective difficulty level. From these results, the validity of this proposed model as the model for the estimation of the amount of mental stress was indicated.