A power supply device supplying power to a semiconductor light-emitting element in response to a power-activation of the power supply device and a dimming signal (VDIM) output from dimming signal generation means, the power supply device having a control circuit and comprising: control means (30-33, 35-45) configured to receive the dimming signal (VDIM) and generate a power control signal (Vcont) for controlling the power supplied to the semiconductor light-emitting element, wherein the control means - generates the power control signal (Vcont) from the dimming signal (VDIM) or by use of a reference signal (Vref) in place of the dimming signal (VDIM), the power control signal (Vcont) being generated at a predetermined level, which does not cause the semiconductor light-emitting element to emit light or causes the semiconductor light-emitting element to emit light with a predetermined light amount and the power control signal (Vcont) being generated for a predetermined time period from the power-activation of the power supply device at an operable level of the control circuit, and - generates the power control signal (Vcont) depending on the dimming signal (VDIM) to dim the semiconductor light-emitting element in accordance with the dimming signal after the predetermined time period lapsed; and DC output generation means (15-18, 25) configured to - receive an AC power, - convert the AC power into a DC power in response to the power control signal (Vcont), and - output the DC power to the semiconductor light-emitting element according to the power control signal (Vcont) to cause the semiconductor light-emitting element to emit light. control means (30-33, 35-45) configured to receive the dimming signal (VDIM) and generate a power control signal (Vcont) for controlling the power supplied to the semiconductor light-emitting element, wherein the control means - generates the power control signal (Vcont) from the dimming signal (VDIM) or by use of a reference signal (Vref) in place of the dimming signal (VDIM), the power control signal (Vcont) being generated at a predetermined level, which does not cause the semiconductor light-emitting element to emit light or causes the semiconductor light-emitting element to emit light with a predetermined light amount and the power control signal (Vcont) being generated for a predetermined time period from the power-activation of the power supply device at an operable level of the control circuit, and - generates the power control signal (Vcont) depending on the dimming signal (VDIM) to dim the semiconductor light-emitting element in accordance with the dimming signal after the predetermined time period lapsed; and - generates the power control signal (Vcont) from the dimming signal (VDIM) or by use of a reference signal (Vref) in place of the dimming signal (VDIM), the power control signal (Vcont) being generated at a predetermined level, which does not cause the semiconductor light-emitting element to emit light or causes the semiconductor light-emitting element to emit light with a predetermined light amount and the power control signal (Vcont) being generated for a predetermined time period from the power-activation of the power supply device at an operable level of the control circuit, and - generates the power control signal (Vcont) depending on the dimming signal (VDIM) to dim the semiconductor light-emitting element in accordance with the dimming signal after the predetermined time period lapsed; and DC output generation means (15-18, 25) configured to - receive an AC power, - convert the AC power into a DC power in response to the power control signal (Vcont), and - output the DC power to the semiconductor light-emitting element according to the power control signal (Vcont) to cause the semiconductor light-emitting element to emit light. - receive an AC power, - convert the AC power into a DC power in response to the power control signal (Vcont), and - output the DC power to the semiconductor light-emitting element according to the power control signal (Vcont) to cause the semiconductor light-emitting element to emit light.