To provide a pulse width modulation system that can enhance transmission efficiency and recording efficiency of data.

The pulse width modulator is provided with a period detection means that measures the period of a signal to be modulated, a peak detection means that measures the maximum level of the signal to be modulated at the period, and a pulse generating means that generates a pulse with a width corresponding to either of the period and the maximum level and a pulse with a width corresponding to the other of the period and the maximum level. Or the pulse width modulator is also provided with a multiplier means that multiplies the period by a multiple of n and outputs the result to the pulse generating means and with a multiplier means that multiplies the maximum level by a multiple of m and outputs the result to the pulse generating means and the pulse generating means may generate a pulse on the basis of the period multiplied by n and the maximum level multiplied by m. In the case of n, m<1, the transmission efficiency can be much more enhanced.