A lighting control device (1, 1A, 1B), comprising: a pair of input terminals (11, 12) electrically connected between a series connection of an illumination load and an AC power supply; a bidirectional switch (2, 2A) configured to switch between conduction and non-conduction of a bidirectional current between the pair of input terminals (11, 12); a phase detector configured to detect a phase of an AC voltage (Vac) of the AC power supply; characterized in that the lighting control device (1, 1A, 1B) further comprises: an inputter configured to receive a dimming level specifying a magnitude of a light output of the illumination load; a power supply electrically connected between the pair of input terminals (11, 12) and configured to be supplied with electric power from the AC power supply to generate control electric power; a voltage detector configured to detect a voltage of the control electric power; a controller (6, 6B) coupled to the phase detector and the inputter, the controller (6, 6B) being configured to be supplied with the control electric power from the power supply to operate and to control the bidirectional switch (2, 2A) based on a detection signal from the phase detector so as to switch the bidirectional switch (2, 2A) from an ON state to an OFF state at a switching time point (t 2) when a variable time corresponding to the dimming level elapses from a starting point of a half period of the AC voltage (Vac); and a stopper configured to be controlled by the controller (6, 6B) so as to halt generation of the control electric power by the power supply when the voltage detected by the voltage detector is higher than or equal to a prescribed threshold (Vth1, Vth2) during an OFF time period from the switching time point to an end time point of the half period, wherein the OFF time period is a time period during which the bidirectional switch (2, 2A) is in the OFF state, and wherein the phase detector is configured to output the detection signal when the phase detector detects a zero crossing point of the AC voltage (Vac), and wherein the controller (6, 6B) is configured to estimate a zero crossing point of the AC voltage (Vac) of at least the half period ahead in future as a virtual zero crossing point each time the controller (6, 6B) receives the detection signal from the phase detector, and wherein the controller (6, 6B) is configured to generate a virtual signal at the timing of the virtual zero crossing point, and wherein, in the event the phase detector fails to detect the zero crossing point of the AC voltage (Vac), the controller (6, 6B) is configured to control the bidirectional switch based on the virtual signal instead of the detection signal from the phase detector. a pair of input terminals (11, 12) electrically connected between a series connection of an illumination load and an AC power supply; a bidirectional switch (2, 2A) configured to switch between conduction and non-conduction of a bidirectional current between the pair of input terminals (11, 12); a phase detector configured to detect a phase of an AC voltage (Vac) of the AC power supply; an inputter configured to receive a dimming level specifying a magnitude of a light output of the illumination load; a power supply electrically connected between the pair of input terminals (11, 12) and configured to be supplied with electric power from the AC power supply to generate control electric power; a voltage detector configured to detect a voltage of the control electric power; a controller (6, 6B) coupled to the phase detector and the inputter, the controller (6, 6B) being configured to be supplied with the control electric power from the power supply to operate and to control the bidirectional switch (2, 2A) based on a detection signal from the phase detector so as to switch the bidirectional switch (2, 2A) from an ON state to an OFF state at a switching time point (t 2) when a variable time corresponding to the dimming level elapses from a starting point of a half period of the AC voltage (Vac); and a stopper configured to be controlled by the controller (6, 6B) so as to halt generation of the control electric power by the power supply when the voltage detected by the voltage detector is higher than or equal to a prescribed threshold (Vth1, Vth2) during an OFF time period from the switching time point to an end time point of the half period, wherein the OFF time period is a time period during which the bidirectional switch (2, 2A) is in the OFF state, and wherein the phase detector is configured to output the detection signal when the phase detector detects a zero crossing point of the AC voltage (Vac), and wherein the controller (6, 6B) is configured to estimate a zero crossing point of the AC voltage (Vac) of at least the half period ahead in future as a virtual zero crossing point each time the controller (6, 6B) receives the detection signal from the phase detector, and wherein the controller (6, 6B) is configured to generate a virtual signal at the timing of the virtual zero crossing point, and wherein, in the event the phase detector fails to detect the zero crossing point of the AC voltage (Vac), the controller (6, 6B) is configured to control the bidirectional switch based on the virtual signal instead of the detection signal from the phase detector.