A server apparatus includes a fixing mechanism and a holding casing having a fixing member. The fixing mechanism includes a containing casing having a guiding slot and an engaging hole, an actuator having a driving member and pivoted to the containing casing to be movable between a first position and a second position, and a driven structure. The driven structure has a driven member and a first slot and is slidable on the holding casing. When the engaging hole is engaged with the fixing member and the actuator moves to the first position, the driving member slides along the first slot to drive the driven structure to a mounting position, so as to slide the driven member along the guiding slot.