To improve a knapsack type bag by reducing the weight, lowering the manufacturing cost and increasing safety during commutation to and from school for students or to and from office for general people.

A fabric using reclaimed thread of PET bottles is used for main members of a knapsack type bag A including the front 1, the back 2, the upper gusset 7, a bottom gusset 5, side gussets 4, the upper lid 3, and the like, in place of a conventional leather or synthetic leather, considering the environment. As a result, the weight could be reduced and the manufacturing cost could be lowered. Concerning improvement of ease of use, reflective plates 3a1, 3a2, 4a, and 10a are attached to the upper lid 3, the side gussets 4 and carrying belts 10 to avoid the risk of students or general people meeting a traffic accident during commutation to and from school or office. In addition, as a storage case has a shape of approximately parallelepiped or of four-side pyramid to prevent it from deforming, it is convenient for storing square documents.