To effectively use a space and sufficiently secure the capacity of an oil pan by attaching an exhaust gas sensor on any one of two front collecting pipes of an engine exhauster in which four exhaust pipes are collected to two front collecting pipes and further collected by one rear collecting pipe.

An exhaust gas sensor 33 is attached to a left front collecting pipe 31L out of right and left front collecting pipes 31L of an engine exhauster 22 in which four exhaust pipes 23a to 23d extending from the front surface of an engine 16 are collected by two front collecting pipes 31L and further collected by one rear collecting pipe 32. The left front collecting pipe 31L having the exhaust gas sensor 33 is arranged on the opposite side to a clutch device with respect to the center of a vehicle body, and the exhaust gas sensor 33 is arranged in such a position as to not interfere the flat shape of the oil pan 30 in plan view. Therefore, a space under the engine 16 can be effectively used, and the capacity of the oil pan 30 can be sufficiently secured.