An alarm unit comprising: a light emitting section; a battery power supply; a voltage booster circuit that boosts a voltage from the battery power supply to thereby generate a boosted voltage; a light emission control section that supplies the boosted voltage of a boosted voltage retention capacitor charged by the voltage booster circuit to the light emitting section, and thereby intermittently drives light emission; a light receiving section that receives light from the light emitting section having been diffused by smoke; a conversion circuit that converts a received light signal from the light receiving section into received light data; a fire hazard detection section that detects a fire hazard based on the received light data from the conversion circuit; an alarm section that outputs an alarm based on a fire hazard detection signal from the fire hazard detection section; a reference voltage circuit that generates a reference voltage for the voltage booster circuit and the conversion circuit; a processor circuit that realizes functions of the light emission control section and the fire hazard detection section by executing a program; and a clock circuit that outputs a clock signal for operating the voltage booster circuit, the light emission control section, the processor circuit and the conversion circuit, characterised in that the alarm unit further comprises a control logic circuit for supplying and stopping clock signals to the voltage booster circuit and to the processor circuit, wherein the processor circuit, the voltage booster circuit, the conversion circuit, the reference voltage circuit, the clock circuit, and the control logic circuit are provided in an integrated circuit, wherein the control logic circuit is configured to supply the clock signal to the voltage booster circuit in a state where a clock signal supply to the processor circuit is stopped, wherein after completion of a voltage boosting operation the control logic circuit is configured to stop the clock signal supply to the voltage booster circuit, and to switch to the clock signal supply to the processor circuit, wherein after completing a processing by the light emission control section and the fire hazard detection section, the processor circuit is configured to output a control signal to the control logic circuit, and wherein while maintaining the clock signal supply to the voltage booster circuit in a stop state, the clock signal supply to the processor circuit is also stopped, and the control logic circuit enters a sleep mode where the clock signal supply to the processor circuit and the voltage booster circuit is stopped. a light emitting section; a battery power supply; a voltage booster circuit that boosts a voltage from the battery power supply to thereby generate a boosted voltage; a light emission control section that supplies the boosted voltage of a boosted voltage retention capacitor charged by the voltage booster circuit to the light emitting section, and thereby intermittently drives light emission; a light receiving section that receives light from the light emitting section having been diffused by smoke; a conversion circuit that converts a received light signal from the light receiving section into received light data; a fire hazard detection section that detects a fire hazard based on the received light data from the conversion circuit; an alarm section that outputs an alarm based on a fire hazard detection signal from the fire hazard detection section; a reference voltage circuit that generates a reference voltage for the voltage booster circuit and the conversion circuit; a processor circuit that realizes functions of the light emission control section and the fire hazard detection section by executing a program; and a clock circuit that outputs a clock signal for operating the voltage booster circuit, the light emission control section, the processor circuit and the conversion circuit, characterised in that the alarm unit further comprises a control logic circuit for supplying and stopping clock signals to the voltage booster circuit and to the processor circuit, wherein the processor circuit, the voltage booster circuit, the conversion circuit, the reference voltage circuit, the clock circuit, and the control logic circuit are provided in an integrated circuit, wherein the control logic circuit is configured to supply the clock signal to the voltage booster circuit in a state where a clock signal supply to the processor circuit is stopped, wherein after completion of a voltage boosting operation the control logic circuit is configured to stop the clock signal supply to the voltage booster circuit, and to switch to the clock signal supply to the processor circuit, wherein after completing a processing by the light emission control section and the fire hazard detection section, the processor circuit is configured to output a control signal to the control logic circuit, and wherein while maintaining the clock signal supply to the voltage booster circuit in a stop state, the clock signal supply to the processor circuit is also stopped, and the control logic circuit enters a sleep mode where the clock signal supply to the processor circuit and the voltage booster circuit is stopped.