Tool storage bag

A tool storage bag (1) includes a hexahedral fabric bag body (2) openable only at a top side (2A) or at the top side (2A) and a bottom side (2F), and an interlining material at least provided at three adjoining sides of the bag body (2). The interlining material includes plural flat plates (3A) to (3C) corresponding to the three sides (2A), (2B), B1 (S1, S2). At least one of the flat plates (3A) to (3C) is detachable from a corresponding one of the sides B1 (S1, S2) of the bag body (2), while the bag body (2) is foldable without folding the sides (2A), (2B) provided with the interlining material. The bag body (2) with at least one flat plate detached from the corresponding side is folded down by overlapping, on one (2B) of the unfoldable sides of the bag body (2), the side (2A) other than the above one side and provided with the interlining material.