Packing box

A packing box comprising:

• a box body having a front wall plate member, a rear wall plate member, a plurality of side wall plate members, and a bottom plate member for housing a product;
• a side flap that is connected via a first folding line to an upper end portion of one of the side wall plate members for preventing protrusion of the product;
• a top face lid that is connected via a second folding line to an upper end portion of the rear wall plate member for openably sealing an upper end portion of the box body;
• and
• an insertion piece that is connected to a front end edge of the top face lid via a third folding line and is inserted into the box body for holding the top face lid, the packing box including a slit lock engaging structure that maintains a state in which the top face lid is closed by engaging a slit engaging piece that is a part of the side flap into a slit created by cutting a part of a connection base end of the insertion piece along a direction parallel to the third folding line;
• wherein the top face lid includes a part that can be torn along a tear inducing line extending from a side flap opposing edge of the top face lid to a front end edge of the top face lid so that the part can be held and torn along the tear inducing line by a human hand and be raised up with respect to the top face lid to form a slit lock release gripping piece that can be used for releasing engagement created by the slit lock engaging structure;
• wherein the slit includes a L-shaped cut formed by a first cut extending from a start point on said third folding line, which is a border between the insertion piece and the top face lid, in a direction transverse to said third folding line, toward an edge of the insertion piece for a length that is at least equal to a thickness of the side flap, and a second cut extending in a direction parallel to said third folding line toward a side end of the insertion piece, and the insertion piece is folded with respect to the top face lid for forming the slit;
• wherein the top face lid is locked in a closed condition by the engagement of said slit engagement piece with said slit;
• wherein a part of the top face lid projecting forward from the third folding line when the insertion piece is folded with respect to the top face lid forms an unlock projection piece that is able to abut against the slit-engaging piece in the slit when the slit lock release gripping piece is raised up to release the engagement created by the slit lock engaging structure;
• and
• wherein said top face lid is openable by a sequence of steps, said steps consisting of tearing said part of the top face lid along said tear inducing line and raising said part up with respect to the top face lid to form said slit lock release gripping piece, manually rotating said part upward and forward about said third folding line, thereby causing said unlock projection piece to abut said slit engaging piece and disengage said slit engaging piece from said slit, and manually pulling upward on said slit lock release gripping piece to remove the insertion piece from the box body and raise the top face lid.