PURPOSE: To protect a rear cover and facilitate oil filler by installing a standing handle which is vertically wide along the lower edge of a driver's seat, in an oil filler port device which is constituted so that the lower part of a driver's seat is covered by a rear cover made of synthetic resin and the oil filler port of a fuel tank is formed on the side surface below the driver's seat.

CONSTITUTION: A standing handle 64 which has a U-shape in a plane view is installed so as to surround the left right parts and rear lower edge of a driver's seat. The standing handle 64 is formed vertically wide at least at the left and right side parts, and a key insertion hole 72 and a fuel filler hole 74 are formed. The position of the fuel filler hole 74 is set so as to be close to the oil filler port of a fuel tank. Accordingly, the deterioration of quanlity and color change of a rear cover due to the oil in oil sypply can be prevented.