To suppress current fluctuations upon commencement of driving and prolong lifespan by reducing electric stress caused by current fluctuations.A glow plug 1, a glow switch 2, and a stabilizing coil 3 are series-connected, and upon commencement of the driving of the glow plug 1, a repetition frequency of PWM signals that control the opening and closing of the glow switch 2 is made into a higher frequency than a repetition frequency in a normal drive state and the opening and closing of the glow switch 2 is controlled (S104), and when a predetermined drive shift condition has been met (S106), the repetition frequency of the PWM signals is returned to the frequency during normal driving and the opening and closing of the glow switch 2 is controlled (S108), whereby the current upon commencement of driving is smoothed and the occurrence of an instantaneous large current is suppressed.