A base plate is a portion of a housing of a disk drive apparatus, including a base body being a casting product, and an electrodeposition coating film covering at least a portion of a surface of the base body. The base body includes a bottom plate rectangular as viewed from an axial direction, a pivot post, and a protrusion. The bottom plate extends perpendicular to a rotation axis of a disk that extends vertically and a swing axis of a head that is disposed in a different position from the rotation axis and that extends vertically. The head reads or writes information from or to the disk. The pivot post protrudes upward from an upper surface of the bottom plate along the swing axis. The protrusion is provided protruding radially outward from a peripheral surface of the pivot post and protruding to the upper surface of the bottom plate.