Lamp socket

The invention relates to a lamp holder holding a lamp such as a high-intensity discharge lamp and so on, which are used as automotive headlights. A lamp holder includes a fit recess for a lamp plug-fitted purpose, a high-voltage side terminal arranged at any one of a central section of the fit recess and a peripheral section surrounding the central section of the fit recess, a low-voltage side terminal arranged at the other, an insulation seal member insulating between the low-voltage side terminal and the high-voltage side member, and at least one projection projected outwardly from an outer peripheral wall of the insulation seal member as to make into contact with an inner peripheral wall of a fit section of the lamp plug side.