To allow an on-vehicle meter or an alarm lamp to display an alarm with good visibility as necessary.

A light source device has an LED having polarities; a circuit board 5 electrically connected to the LED and having a means for blinking the LED at 0.5 to 10 Hz; a socket main body 2 storing the circuit board; an inner terminal part stored in the socket main body and making contact with a contact of the circuit board to make an electrical connection therewith; and contact terminals 9, 10 having external terminals 9a, 10a electrically connected to the inner terminal part and fixed in place while projecting outside of the socket main body.