A work vehicle transmission comprising: a plurality of transmission shafts that extend parallel with each other in a front-rear direction of a vehicle body, the plurality of transmission shafts including a speed change shaft, a deceleration shaft; and an intermediate shaft arranged between the speed change shaft and the deceleration shaft, a main transmission apparatus including: a first transmission mechanism having a plurality of speed change gear sets and a plurality of speed change multi-disc clutches, the speed change gear sets having first speed change gears (56A-59A) arranged on the speed change shaft and second speed change gears (56B-59B) arranged on the intermediate shaft for transmitting motive power from the speed change shaft to the intermediate shaft, and the speed change multi-disc clutches being arranged adjacent in the front-rear direction on the speed change shaft and engage and disengage power transmission to the plurality of speed change gear sets; and a second transmission mechanism, the number of speeds of the second transmission mechanism being smaller than the number of speeds of the first transmission mechanism, and the second transmission mechanism having a plurality of deceleration gear sets (64,65), and a plurality of deceleration multi-disc clutches (66,67), the deceleration gear sets (64,65) having first deceleration gears (64A, 65A) arranged on the intermediate shaft and second deceleration gears (64B, 65B) arranged on the deceleration shaft for transmitting motive power from the intermediate shaft to the deceleration shaft, and the deceleration multi-disc clutches (66,67) being arranged on the deceleration shaft and engage and disengage power transmission to the plurality of deceleration gear sets (64,65), wherein the plurality of speed change multi-disc clutches are arranged parallel with the plurality of deceleration multi-disc clutches (66,67) so as to be adjacent in a diameter direction thereof. a plurality of transmission shafts that extend parallel with each other in a front-rear direction of a vehicle body, the plurality of transmission shafts including a speed change shaft, a deceleration shaft; and an intermediate shaft arranged between the speed change shaft and the deceleration shaft, a main transmission apparatus including: a first transmission mechanism having a plurality of speed change gear sets and a plurality of speed change multi-disc clutches, the speed change gear sets having first speed change gears (56A-59A) arranged on the speed change shaft and second speed change gears (56B-59B) arranged on the intermediate shaft for transmitting motive power from the speed change shaft to the intermediate shaft, and the speed change multi-disc clutches being arranged adjacent in the front-rear direction on the speed change shaft and engage and disengage power transmission to the plurality of speed change gear sets; and a second transmission mechanism, the number of speeds of the second transmission mechanism being smaller than the number of speeds of the first transmission mechanism, and the second transmission mechanism having a plurality of deceleration gear sets (64,65), and a plurality of deceleration multi-disc clutches (66,67), the deceleration gear sets (64,65) having first deceleration gears (64A, 65A) arranged on the intermediate shaft and second deceleration gears (64B, 65B) arranged on the deceleration shaft for transmitting motive power from the intermediate shaft to the deceleration shaft, and the deceleration multi-disc clutches (66,67) being arranged on the deceleration shaft and engage and disengage power transmission to the plurality of deceleration gear sets (64,65), a first transmission mechanism having a plurality of speed change gear sets and a plurality of speed change multi-disc clutches, the speed change gear sets having first speed change gears (56A-59A) arranged on the speed change shaft and second speed change gears (56B-59B) arranged on the intermediate shaft for transmitting motive power from the speed change shaft to the intermediate shaft, and the speed change multi-disc clutches being arranged adjacent in the front-rear direction on the speed change shaft and engage and disengage power transmission to the plurality of speed change gear sets; and a second transmission mechanism, the number of speeds of the second transmission mechanism being smaller than the number of speeds of the first transmission mechanism, and the second transmission mechanism having a plurality of deceleration gear sets (64,65), and a plurality of deceleration multi-disc clutches (66,67), the deceleration gear sets (64,65) having first deceleration gears (64A, 65A) arranged on the intermediate shaft and second deceleration gears (64B, 65B) arranged on the deceleration shaft for transmitting motive power from the intermediate shaft to the deceleration shaft, and the deceleration multi-disc clutches (66,67) being arranged on the deceleration shaft and engage and disengage power transmission to the plurality of deceleration gear sets (64,65), wherein the plurality of speed change multi-disc clutches are arranged parallel with the plurality of deceleration multi-disc clutches (66,67) so as to be adjacent in a diameter direction thereof.