Abstract: An illuminator includes an illuminator frame having a cut-out portion in which a light source unit is removably positioned. The light source unit includes a cold-lamp light source supported in a plate-like member of the unit's frame. The plate-like member has extended portions which are also plate-like for fitting into guide slits formed in a light source unit supporting member of the illuminator. The supporting member has a retainer which helps hold the plate-like extensions of the plate-like member of the light source unit. The illuminator includes a power supply linked with a connector positioned so that when the light support unit is inserted into the illuminator in its proper position, a connector provided on the light source unit will connect the light source to the power supply. Thus, the light source unit can be removed from or inserted into the illuminator in a single step process.