PROBLEM TO BE SOLVED: To display three colors of a color of light emitted by a first light-emitting element, a mixed color of colors of light emitted by the first light-emitting element and a second light-emitting element and a color of light emitted by the second light-emitting element, in accordance with a change of a power supply voltage, by means of the two light-emitting elements.SOLUTION: A green LED 21 and a red LED 22 are provided. The LEDs 21, 22 are disposed so as to mix light emitted by the LEDs, respectively, and connected in parallel to a power supply line 23 from a battery 7. A first circuit 24 including the green LED 21 is connected to the power supply line 23 so as to turn on the green LED 21 within a first voltage range equal to or more than a voltage value dropped from a battery voltage in the case where remaining battery power is maximum, just by a predetermined value. A second circuit 25 including the red LED 22 is connected to the power supply line 23 so as to turn on the red LED 22 withi
