PURPOSE: To obtain a strong waist porch of good appearance used also for a knapsack, by a method wherein the knapsack is folded, made small, and stowed in an auxiliary sack, and a second fastener is closed, and thus the knapsack is convertible into the waist porch.

CONSTITUTION: The lower hems of both a front cloth 1 and a rear cloth 2 are sewed together with the peripheral hem of a bottom cloth 3, and both the side hems of the front cloth 1 are sewed together with both the side hems of the rear cloth 2, and thus a waist porch main body 4 is composed. Both the upper hem of the rear cloth 2 and the rear hem of a cover cloth 5 are sewed, and a first fastener 6 is fixed between the front hem of the cover cloth 5 and the upper hem of the front cloth 1, and thus the waist porch main body 4 is made openable or closable. On the other hand, a second fastener 8 is fixed at the upper part behind waste porch main body 4, and a fastener tape 8a is sewed at the part sewed between the rear cloth 2 and the cover cloth 5, and the other fastener tape 8b is sewed on a back cloth 10. This back cloth 10 is converted into a part of a knapsack front cloth, and an auxiliary bag S2 is formed between the rear cloth 2 and the back cloth 10, and a knapsack 11 is folded and stowed therein.