A pulse width modulator comprising: a first voltage to current converting section for converting an AC voltage signal to be inputted into a first electric current expressed by a linear function having an inclination proportional to an amplitude of the AC voltage signal; a second voltage to current converting section for converting the AC voltage signal into a second electric current having an inclination opposite to the first electric current; a first charging/discharging control section for repeating a charging/discharging operation for charging a first electric charge storage section with the first electric current for a predetermined time and discharging the electric charges stored in the first electric charge storage section with a predetermined constant current (Id) in a period twice as long as the predetermined time; a second charging/discharging control section for repeating a charging/discharging operation for charging a second electric charge storage section with the second electric current for the predetermined time and discharging the electric charges stored in the second electric charge storage section with the predetermined constant current (Id) in the period with shifting the predetermined time for the charging/discharging operation of the first electric charge storage section through the first charging/discharging control section; a first discharge timing detecting section for detecting the discharge end timing every time when the discharge of the stored electric charges in the second electric charge storage section is ended; a second discharge timing detecting section for detecting the discharge end timing every time when the discharge of the stored electric charges in the first electric charge storage section is ended; and a pulse width modulation signal generation section for generating a pulse whose pulse width is a time interval between a first discharge end timing detected by the first discharge timing detecting section and a subsequent second discharge end timing detected by the second discharge timing detecting section, and outputting a signal of a pulse string as a pulse width modulation signal (S PWM). a first voltage to current converting section for converting an AC voltage signal to be inputted into a first electric current expressed by a linear function having an inclination proportional to an amplitude of the AC voltage signal; a second voltage to current converting section for converting the AC voltage signal into a second electric current having an inclination opposite to the first electric current; a first charging/discharging control section for repeating a charging/discharging operation for charging a first electric charge storage section with the first electric current for a predetermined time and discharging the electric charges stored in the first electric charge storage section with a predetermined constant current (Id) in a period twice as long as the predetermined time; a second charging/discharging control section for repeating a charging/discharging operation for charging a second electric charge storage section with the second electric current for the predetermined time and discharging the electric charges stored in the second electric charge storage section with the predetermined constant current (Id) in the period with shifting the predetermined time for the charging/discharging operation of the first electric charge storage section through the first charging/discharging control section; a first discharge timing detecting section for detecting the discharge end timing every time when the discharge of the stored electric charges in the second electric charge storage section is ended; a second discharge timing detecting section for detecting the discharge end timing every time when the discharge of the stored electric charges in the first electric charge storage section is ended; and a pulse width modulation signal generation section for generating a pulse whose pulse width is a time interval between a first discharge end timing detected by the first discharge timing detecting section and a subsequent second discharge end timing detected by the second discharge timing detecting section, and outputting a signal of a pulse string as a pulse width modulation signal (S PWM).