In a motorcycle in which a rear fork is swingably provided on a vehicle body frame with a power unit, a rear wheel is provided at a rear end of the rear fork, a drive shaft is provided between a gear case on a lateral side of the rear wheel and an output shaft of the power unit, and output power of the power unit is transmitted to the rear wheel through the drive shaft and the gear case. The rear fork extends along a lateral side of the rear wheel and has an arm through which the drive shaft passes. The arm has a tubular base part with a closed cross section, and a rear part with an open cross section through which the drive shaft passes. The base part has a thick-walled area at the rear end of the base part.