A attachment structure enabling more efficient work in performing maintenance of a fan of a fan unit and a more stable electrical connection between a main body of an electrical equipment and a fan unit. A attachment structure configured to detachably attach a fan unit including a fan and a casing housing the fan to/from a main body of an electrical equipment includes a guide mechanism configured to guide a slide motion of sliding the casing in one direction relative to the main body to dispose the casing at a mounting position, and a retaining mechanism configured to restrict movement of the casing relative to the main body in a direction opposite the one direction when the casing is disposed at the mounting position by the slide motion.