A fastening structure of an onboard apparatus to be fastened to a vehicle body includes a support member that is fastened to the vehicle body to support the onboard apparatus and has a protruding section protruding rearward beyond a rear face of the onboard apparatus, and a bracket having a front fastening section to be fastened to a lower face of a rear section of the onboard apparatus, a rear fastening section to be fastened to the protruding section of the support member, and a fragile section provided between the front fastening section and the rear fastening section. By an external force from a front side of the onboard apparatus, the fragile section is deformed and the rear section of the onboard apparatus is moved upward using the rear fastening section as a fulcrum.