A protective cover for a rotary electric machine including: a bottom portion formed into an approximately circular shape; a side wall extending from the bottom portion along an outer periphery thereof; and an opening portion, of approximately circular shape and formed by an end of the side wall, wherein the side wall has a plurality of guide ribs formed on an inner side thereof and arranged apart from each other along the outer periphery of the bottom portion, wherein each of the guide ribs has a chamfered portion at an end on a side closer to the opening portion, and wherein each of the guide ribs has a height of a top portion of each of the plurality of guide ribs from the side wall allows the top portion to contact a side surface of the component when the protective cover is mounted to the rotary electric machine.