To provide a new pocket device for knapsack, bag and the like, which is convenient for elementary and junior high school students who insert long things such as a recorder, etc., thereinto in such a manner as to raise them for carrying them.

A pocket component piece, wherein right and left gusset parts are mounted on both of right and left side edges of a main plate part and which has a seam allowance part at the lower side edge of the main plate part and is manufactured of leather, a synthetic resin, a thick texture, etc., is mounted on a pocket fitting portion of a main body of the knapsack, the bag or the like. The boundary parts between the main plate part and the gusset parts are made mountain fold condition parts, lengthwise central line parts of the gusset parts are made valley-folded condition parts, and valley bottom parts of both side of the valley-folded condition parts are stitched to from the twofold gusset parts. The seam allowance part is seamed lapped in a reversed condition at the lower edge of the pocket fitting portion, and then the boundary part between the main plate part and the seam allowance part is folded to put the whole pocket part in such a condition as to be turned up. Thereby, the pocket part is put in such a condition to be positioned outside the pocket fitting portion, and the outer side edges of the gusset parts are seamed at the right and left parts of the pocket sitting portion in such a condition as the gusset parts are kept two-fold.