To provide a lighter knapsack which is produced seeking the safety on use from a material to meet requirements for environmental preservation.

The body 2 of an oblong type knapsack with the top opened, a lid piece 4 for opening or closing the opening with one end thereof fixed near the upper end of a back part 3 of the body 2 of the knapsack, a front pocket 6 fastened on the front part 5 of the body 2 of the knapsack and a pair of right and left shoulder straps 8 and 8 linked to an upper part of the back part 3 of the body 2 of the knapsack and the bottom part 7 thereof are made using reproduced yarns from polyethylene terephthalate bottles. Both side parts 9 and 9 of the body 2 of the knapsack with no template make a clearance margin stretchable between the back part 3 and the front part 5 and a belt 31a for binding both flaps 30 and 30b fastened on both the side pars 9 and 9 of the body 2 of the knapsack at the opening of the body 2 of the knapsack is made to cross a belt 31b for binding the front part 5 and the back part 3 of the body 2 of the knapsack to prevent articles from being popped out of a housing part of the body 2 of the knapsack while a reflector 16 is provided on the front of the pair of shoulder straps 8 and 8 linked to the upper part of the back part 3 and the bottom part 7 of the body 2 of the knapsack, and on both the side parts 9 and 9 of the body 2 of the knapsack and the lid piece 4.