Abstract: An activity intensity measurement device comprises an accelerator, a sampling means, a representative value calculation means, a sampling means, a representative value calculation means, and an activity intensity determination means. The sampling means is configured to sample discrete values from the detected acceleration. The representative value calculation means is configured to calculate the representative value from the discrete values of a plurality of the acceleration. The activity intensity determination means is configured to determine the activity intensity on the basis of the calculated representative value. The representative value calculation means is configured to calculate the representative value at intervals of unit period corresponding to the user's particular activity. Consequently, all of the user's particular activity is reflected to the representative value. Therefore, this activity intensity measurement device is configured to calculate exact activity intensity.