87 has arranged from adjacent the second partition 18 to front a superlow speed input gear 88 a low speed gear 89 a high speed gear 90 and a superlow speed output gear 91 which are rotatable relative to the propelling shaft 87 in addition a front wheel drive gear 92 is fixed to the propelling shaft 87 forwardly of the above gears the low speed gear 89 and high speed gear 90 on the propelling shaft 87 are in constant mesh with the low speed gear 85 and high speed gear 86 on the change speed output shaft 58 respectively the superlow speed input gear 88 and low speed gear 89 on the propelling shaft 87 are twin gears the transmission case 2 further includes an intermediate shaft 93 supported to be rotatable through bearings and extending parallel to the propelling shaft 87 the intermediate shaft 93 has gears 94 and 95 mounted to be rotatable therewith and in constant mesh with the superlow speed input gear 88 and superlow speed output gear 91 the propelling shaft 87 has a high and low speed switching clutch 96 mounted thereon between the low speed gear 89 and high speed gear 90 the high and low speed switching clutch 96 is a claw clutch having.