The embodiments of the present invention relate to a double-side printer system in which two thermal heads printing print data on a front face and a back face of a thermal recording paper in which thermo-sensitive layers are formed on both sides are provided, and when these thermal heads are driven in accordance with the print data, temperatures of these thermal heads are sensed in order to vary print densities of the data to be printed, and ON/OFF times for electrical connections are controlled with respect to heater elements of the respective thermal heads, and to a control method thereof.