A signal lamp apparatus with a lamp burnout detecting circuit has a right turn signal lamp group and a left turn signal lamp group which are connected to a power source through a turn signal switch and a relay contact coupled in parallel with a burnout detecting resistor. Each of the lamp groups includes a plurality of signal lamps connected in parallel with one another. The apparatus includes a comparator which produces an output signal when the voltage across the signal lamp group is higher than a predetermined voltage, and a device which produces a burnout signal when the comparator has an output signal after lights-out, for example, after 20 to 100 m sec since the relay contact is opened. With such an arrangement, the burnout of the signal lamp or lamps may be detected while the signal light lamp group is flashing.