A flat-type fluorescent lamp is used as a light source of a color thermal printer. The flat-type fluorescent lamp has a yellow luminescent surface for emitting yellow fixing rays, and a magenta luminescent surface for emitting magenta fixing rays. The respective luminescent surfaces are disposed back to back and are selectively activated by a lamp driving circuit. The flat-type fluorescent lamp is rotatable between a first position where the yellow luminescent surface confronts a recording surface of a color thermosensitive recording paper, and a second position where the magenta luminescent surface confront the recording surface of the recording paper.