PURPOSE: To make temp. elevation of a heat generating element const. and to obtain a stable thermal recording by controlling the intermittent ratio of a pulse by taking fluctuation of loading into consideration.

CONSTITUTION: Energization of electricity to a thermal head is started (S200) and when time Δt passes through (S220:YES), an off time in accordance with the value of detected electric voltage of a successive electric voltage detecting part is determined based on the table of ROM (S240). Then, during the second time Δt passes through when an on time of an applied pulse passes through (S250:YES), a CPU controls the driving circuit of the thermal head and performs off processing and makes a pulse applied to a heat generating element off. Then, when the off time determined by S240 (S270:YES), increment of the value of counting of a counter is made by one (S280). The, when this value of counting is different from (the applied pulse width/the time Δt+1) (S290:NO), the applied pulse is made on (S300) and the processing after S230 is executed again.