A brake light sensor module includes: a retainer which is provided to move together with an operation element of a master cylinder in response to a depression of a brake pedal; an operation rod which is connected to the retainer so as to move together with the retainer; an elastic member which is installed in the master cylinder; a signal transmitting element which is installed in the master cylinder, one end of the signal transmitting element being elastically supported by the elastic member, and the other end of the signal transmitting element being supported by the operation rod; and a sensor which is installed in the master cylinder so as to be operated by the signal transmitting element.