To provide a fixing device for arc tubes which prevents, as much as possible, deformation produced in degreasing or baking an arc tube made of aluminum nitride and can supply a reducing agent sufficiently and nearly uniformly to the arc tube during baking.

A holder for ceramic moldings which holds a ceramic molding 6 in a vertical posture consists of a body 6a composed of a hollow molding and axial parts 6b and 6c protruding from both ends of the body 6a. The axial parts 6b and 6c consist of a pair of frames 20 and 30 having holes 12 and 14 capable of loosely fitting so that the ceramic molding 6 is held in the lower frame 30 with at least a part of the lower portion of the body 6a kept in contact with the frame 30. The hole 14 formed in at least one of the frames is a non-through hole 14 having such a depth as to be capable of containing the axial parts, and the frame 30 having the non-through hole 14 forms another gas-permeable through hole 36.