A fuel tank covering (26) to cover an upper portion of a fuel tank (25) supported by a motorcycle frame structure (FR) covers an intermediate portion of the fuel tank (25) ranging from a front end portion to a rear end portion with respect to a direction widthwise of the motorcycle, and includes a shielding portion (36) configured to cover a mounting area at a front portion where a key cylinder (35) disposed forwardly of the fuel tank (25) is mounted on the motorcycle frame structure (FR).

A fuel tank cap includes a seal cap body and a detaching-proof unit. The cap body has a handheld wall and a surrounding wall that extends from the handheld wall and that is formed with an engaging groove. The detaching-proof unit includes a ring sleeve member and a connection member. The ring sleeve member has an outer ring wall that surrounds the surrounding wall, and a resilient wall that extends the outer ring wall and that is engaged resiliently with the engaging groove. The connection member is connected to the ring sleeve member to be connected to a cap installation portion of a vehicle body.