A GCU (21) includes calibration means (33) which supplies electric current to a glow plug (1) when an internal combustion engine EN to which the glow plug (1) is attached is stopped, to thereby obtain a pre-correction target resistance of the glow plug (1). The calibration means (33) supplies a predetermined first electric power to the glow plug (1) in a predetermined first energization period, and supplies a predetermined second electric power to the glow plug (1) after the first energization period. The second electric power is set such that, when the second electric power is supplied to the glow plug (1) and the temperature of the glow plug (1) becomes saturated, the temperature of the glow plug (1) becomes equal to the target temperature. Further, the first electric power is greater than the second electric power.