A heater energization control apparatus. When an engine is stopped, a microcomputer of a GCU enters a power save mode. When the microcomputer returns to a normal mode in response to an interruption signal periodically generated from an interruption timer, the microcomputer supplies electricity to a heating resistor for a short time and obtains its resistance (S19). When the resistance is greater than a first reference value, the microcomputer determines that a glow plug is removed from the engine; that is, the glow plug is being exchanged (S29). The microcomputer sets an exchange flag to “1” (S30), and performs calibration for the heating resistor of a new glow plug after the engine is operated next time (S35). When the current resistance becomes smaller than the past resistance, the microcomputer determines that the glow plug has been exchanged.