a light source unit for an endoscope has a socket to which a plug at the end of a universal code of the endoscope is attached . the socket has a socket body with a recess in which the plug is fitted and socket terminals to which plug terminals are connected . a number of slots opening to the recess are formed in the socket body . the slots extend along the insertion path of the plug terminals and have the socket terminals therein . the socket terminals cannot be directly touched by a finger or the like . when the plug is attached to the socket , the plug terminals come into contact with the socket terminals properly .