An auxiliary arm attaching structure of a stand apparatus 1 includes a front member 3 that is attached to a support arm 2 of the stand apparatus and has a projection 6. The projection projects in a direction different from a longitudinal direction of the support arm and supports an auxiliary arm 8. Supported with the projection, the auxiliary arm is turnable so that an electronic image display unit 9 attached to a front end of the auxiliary arm is turnable to any position around a surgical microscope 4 supported with the front member.
