An electric power converter apparatus includes a case. The case includes a case main body and a lower cover. A recess is formed at a main body floor of the case main body and is covered with the lower cover to form a floor passage. The floor passage includes an upstream passage and a downstream passage. The lower cover includes joint plate portions, a passage plate portion and beads. The joint plate portions are arranged side by side in a width direction of the floor passage while the floor passage is interposed between the joint plate portions. The passage plate portion extends over the joint plate portions in the width direction of the floor passage. Each bead is formed between the passage plate portion and a corresponding one of the joint plate portions and extends in an intersecting direction that intersects the passage plate portion.