An alarm drive circuit comprising: a transformer to be connected to a sound generator; a drive unit that comprises a switch unit interposed between a power supply and the transformer and is configured to turn on/off the switch unit to supply a drive power to the sound generator by converting a power supply voltage into a high-frequency voltage via the transformer; and a control unit configured to perform PWM control by giving a drive signal to the switch unit of the drive unit, characterized by further comprising: a voltage detection unit configured to measure the power supply voltage; a temperature detection unit configured to measure an ambient temperature of the sound generator; and a current detection unit configured to measure consumption current in the sound generator, the control unit being configured to store a threshold of the consumption current associated with the power supply voltage and the ambient temperature, and two or more of pattern tables separated by the threshold, and the control unit being configured to make comparison of the consumption current value measured by the current detection unit with the threshold and select one of the two or more pattern tables based on a result of the comparison, and adjust the drive power with reference to the selected pattern table to keep a sound pressure of a sound outputted from the sound generator constant. a transformer to be connected to a sound generator; a drive unit that comprises a switch unit interposed between a power supply and the transformer and is configured to turn on/off the switch unit to supply a drive power to the sound generator by converting a power supply voltage into a high-frequency voltage via the transformer; and a control unit configured to perform PWM control by giving a drive signal to the switch unit of the drive unit, characterized by further comprising: a voltage detection unit configured to measure the power supply voltage; a temperature detection unit configured to measure an ambient temperature of the sound generator; and a current detection unit configured to measure consumption current in the sound generator, the control unit being configured to store a threshold of the consumption current associated with the power supply voltage and the ambient temperature, and two or more of pattern tables separated by the threshold, and the control unit being configured to make comparison of the consumption current value measured by the current detection unit with the threshold and select one of the two or more pattern tables based on a result of the comparison, and adjust the drive power with reference to the selected pattern table to keep a sound pressure of a sound outputted from the sound generator constant. a voltage detection unit configured to measure the power supply voltage; a temperature detection unit configured to measure an ambient temperature of the sound generator; and a current detection unit configured to measure consumption current in the sound generator, the control unit being configured to store a threshold of the consumption current associated with the power supply voltage and the ambient temperature, and two or more of pattern tables separated by the threshold, and the control unit being configured to make comparison of the consumption current value measured by the current detection unit with the threshold and select one of the two or more pattern tables based on a result of the comparison, and adjust the drive power with reference to the selected pattern table to keep a sound pressure of a sound outputted from the sound generator constant.