A traffic light detecting device comprising: an image capturing unit mounted on a vehicle and configured to capture an image of surroundings of the vehicle; and a traffic light detecting unit configured to detect a traffic light (32, 33) from the image, wherein the traffic light detecting unit includes a reference signal generating unit configured to set reference signals (L01, L02, L03) the number of which is a multiple of three, phases of which are shifted each other by a time obtained by dividing a cycle of an alternating current power of a commercial power supply supplied to the traffic light (32, 33) by the multiple of three, and cycles of which are equal to the cycle of the alternating current power, a phase adjusting unit configured to select, from the reference signals (L01, L02, L03) the number of which is the multiple of three, a reference signal having a phase closest to a phase of the alternating current power, and adjust the phase of the reference signal to the phase of the alternating current power, a synchronized pixel extracting unit configured to extract from the image a synchronized pixel with a luminance which varies in synchronization with the reference signal having the phase adjusted to the phase of the alternating current power, and a traffic light judging unit configured to judge from the synchronized pixel extracted by the synchronized pixel extracting unit whether or not the traffic light (32, 33) is present. an image capturing unit mounted on a vehicle and configured to capture an image of surroundings of the vehicle; and a traffic light detecting unit configured to detect a traffic light (32, 33) from the image, wherein the traffic light detecting unit includes a reference signal generating unit configured to set reference signals (L01, L02, L03) the number of which is a multiple of three, phases of which are shifted each other by a time obtained by dividing a cycle of an alternating current power of a commercial power supply supplied to the traffic light (32, 33) by the multiple of three, and cycles of which are equal to the cycle of the alternating current power, a phase adjusting unit configured to select, from the reference signals (L01, L02, L03) the number of which is the multiple of three, a reference signal having a phase closest to a phase of the alternating current power, and adjust the phase of the reference signal to the phase of the alternating current power, a synchronized pixel extracting unit configured to extract from the image a synchronized pixel with a luminance which varies in synchronization with the reference signal having the phase adjusted to the phase of the alternating current power, and a traffic light judging unit configured to judge from the synchronized pixel extracted by the synchronized pixel extracting unit whether or not the traffic light (32, 33) is present. a reference signal generating unit configured to set reference signals (L01, L02, L03) the number of which is a multiple of three, phases of which are shifted each other by a time obtained by dividing a cycle of an alternating current power of a commercial power supply supplied to the traffic light (32, 33) by the multiple of three, and cycles of which are equal to the cycle of the alternating current power, a phase adjusting unit configured to select, from the reference signals (L01, L02, L03) the number of which is the multiple of three, a reference signal having a phase closest to a phase of the alternating current power, and adjust the phase of the reference signal to the phase of the alternating current power, a synchronized pixel extracting unit configured to extract from the image a synchronized pixel with a luminance which varies in synchronization with the reference signal having the phase adjusted to the phase of the alternating current power, and a traffic light judging unit configured to judge from the synchronized pixel extracted by the synchronized pixel extracting unit whether or not the traffic light (32, 33) is present.