Stop lamp switch abnormality detecting device

A stop lamp switch abnormality detecting device (2) includes a stop lamp switch (26) which is turned on and off in conjunction with ON operation and OFF operation of a brake pedal (25) so as to switch a lighting state of a stop lamp (28); a control determining unit (64) which determines whether a vehicle (1) is suddenly steered; and a control selecting unit (66) which determines whether the stop lamp switch (26) is abnormal based on a state of the stop lamp switch (26) and a determination result of the control determining unit (64), wherein the control selecting unit (66) determines that the stop lamp switch (26) is abnormal when it is determined that the stop lamp switch (26) is maintained in an ON state at the time the control determining unit (64) determines that the sudden steering operation is performed.