PURPOSE: To facilitate maintenance of an air cleaner by forming a communication port which can be opened and closed freely and communicates to the air cleaner from the inside of an accommodation box, on the bottom part of the accommodation box over the air cleaner.

CONSTITUTION: An accommodation box 16 is arranged in the space over an engine unit 4 at the center part of a car body, between a seat 11 and a head pipe 7, and the front and rear edge parts are fixed onto a main frame 6 and a set rail 9, respectively, by the supporting metal fittings 17 and 18. In the accommodation box 16, a part of the upper surface is opened, and the front edge of a box cover 19 is pivotally installed at the front edge of the opened port. A carburetor 20 and an air cleaner 21 are arranged in the longitudinal direction under the accommodation box 16. In such a motorcycle, a communication port 16b is drilled on the bottom part 16a of the accommodation box 16 which nearly corresponds to the upper cover 21a in free opening and closing of the air cleaner 21, and an opening/closing cover 16c is fitted in demountable ways into the communication port 16b.