A lighting control device (1, 1A, 1B), comprising: a pair of input terminals (11, 12) configured to be electrically connected between a series circuit 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); an inputter configured to receive a dimming level specifying a magnitude of a light output of the illumination load; a controller (6, 6B) configured to control the bidirectional switch (2, 2A) so as to retain the bidirectional switch (2, 2A) in an ON state for an on time having a length determined in accordance with the dimming level within a prescribed range in each of half periods of an AC voltage (Vac) of the AC power supply; characterized in that: the controller (6, 6B) comprises a corrector (61, 61B) configured to determine, with reference to a determination condition, whether or not a target waveform which is a voltage waveform input to the pair of input terminals (11, 12) has an anomaly and to correct the prescribed range so as to narrow the prescribed range when the target waveform has the anomaly; and the lighting control device (1, 1A, 1B) further comprises a phase detector configured to output a detection signal to the corrector (61, 61B) when the phase detector detects a zero crossing point (t0, t4) of the AC voltage (Vac), wherein: the controller (6, 6B) is conngured to estimate a zero crossing point (t0, t4) of the AC voltage (Vac) of at least a half period ahead in future based on the detection signal for one time to obtain a virtual zero crossing point and to generate a virtual signal at the virtual zero crossing point, and the corrector (61, 61B) is configured to determine that the target waveform has the anomaly, (i) when the detection signal is irregularly input to the corrector (61, 61B), the determination condition being that the detection signal is regularly input from the phase detector to the corrector (61, 61B) every half period; or (ii) when either one of the detection signal and the virtual signal is irregularly input to the corrector (61, 61B), the determination condition being that at least one of the detection signal and the virtual signal is regularly input to the corrector (61, 61B) every half period. a pair of input terminals (11, 12) configured to be electrically connected between a series circuit 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); an inputter configured to receive a dimming level specifying a magnitude of a light output of the illumination load; a controller (6, 6B) configured to control the bidirectional switch (2, 2A) so as to retain the bidirectional switch (2, 2A) in an ON state for an on time having a length determined in accordance with the dimming level within a prescribed range in each of half periods of an AC voltage (Vac) of the AC power supply; the controller (6, 6B) comprises a corrector (61, 61B) configured to determine, with reference to a determination condition, whether or not a target waveform which is a voltage waveform input to the pair of input terminals (11, 12) has an anomaly and to correct the prescribed range so as to narrow the prescribed range when the target waveform has the anomaly; and to determine, with reference to a determination condition, whether or not a target waveform which is a voltage waveform input to the pair of input terminals (11, 12) has an anomaly and to correct the prescribed range so as to narrow the prescribed range when the target waveform has the anomaly; and the lighting control device (1, 1A, 1B) further comprises a phase detector configured to output a detection signal to the corrector (61, 61B) when the phase detector detects a zero crossing point (t0, t4) of the AC voltage (Vac), wherein: the controller (6, 6B) is conngured to estimate a zero crossing point (t0, t4) of the AC voltage (Vac) of at least a half period ahead in future based on the detection signal for one time to obtain a virtual zero crossing point and to generate a virtual signal at the virtual zero crossing point, and the controller (6, 6B) is conngured to estimate a zero crossing point (t0, t4) of the AC voltage (Vac) of at least a half period ahead in future based on the detection signal for one time to obtain a virtual zero crossing point and to generate a virtual signal at the virtual zero crossing point, and the corrector (61, 61B) is configured to determine that the target waveform has the anomaly, (i) when the detection signal is irregularly input to the corrector (61, 61B), the determination condition being that the detection signal is regularly input from the phase detector to the corrector (61, 61B) every half period; or (ii) when either one of the detection signal and the virtual signal is irregularly input to the corrector (61, 61B), the determination condition being that at least one of the detection signal and the virtual signal is regularly input to the corrector (61, 61B) every half period. (i) when the detection signal is irregularly input to the corrector (61, 61B), the determination condition being that the detection signal is regularly input from the phase detector to the corrector (61, 61B) every half period; or (ii) when either one of the detection signal and the virtual signal is irregularly input to the corrector (61, 61B), the determination condition being that at least one of the detection signal and the virtual signal is regularly input to the corrector (61, 61B) every half period.