A sealing structure includes: a case that stores an in-vehicle electronic component and has an opening; and a first cover member that covers the opening of the case. The case includes: an protrusion member that has a sealing surface protruded to surround the opening; and a rib that is protruded on an opposite side of the opening with the protrusion member interposed therebetween. The rib has a discharge surface that is connected to the sealing surface of the protrusion member. The first cover member has an extension member that extends along the rib. The discharge surface of the rib is located to be lower than the sealing surface of the protrusion member while the case is arranged with the opening facing upward, and the extension member of the first cover member extends to be lower than the discharge surface of the rib.