Provided is a substrate unit that has a simple structure and is able to prevent water that has entered the inside from reaching a mounting surface of the substrate. The substrate unit includes: a substrate, a first casing member that supports the substrate, and a second casing member that is integrated into one piece with the first casing member and is provided on a mounting surface side of the substrate, wherein the second casing member is provided with a protruding portion that protrudes into a housing space that is defined by the first casing member and the second casing member and houses the substrate, and intersects a plane that extends along the mounting surface of the substrate.