To comfortably and easily use a bed to be provided on a cabin rear part of a truck by extending it in width and making bent rises on a reclining seat backrest and a knee stand.

A part of a bed 16 for a truck is constituted free to erect and fall in the cross direction or in the lengthy direction, and it is devised to provide the maximum width by prostrating the part of the bed on the side of a driver's seat at the time of advancing the driver's seat 10 at the time of driving suspension, to avoid an interference with the bed by bending and raising a part of the bed in the rear of the driver's seat 10 at the time of retreating the driver's seat 10 at the time of driving and to form a reclining seat back rest part and a knee stand part by gradually bending and raising a part of the bed.