To provide a packaging box capable of being used as a display box for display, easily assembled, and securely holding a display board for advertising merchandise.

In a packaging box comprising a box body forming piece 12, wherein four boards including a front board 16 are continuously connected to form a cylindrical body, the packaging box comprises: a rear board 50 sectioned by a first folding ruled line 46 in the continuous connection direction and a pair of opening cutting lines 48 from both ends of the first folding ruled line to a front board 16 upper end, in the front board 16; a U-shaped projecting piece 66 having a distal end part 66a directed to an upper end side of the cylindrical body and having a base end part 66b narrowed in width in a mutual approaching direction in the front board 16; a display board 52 extended to a distal end part of the rear board 50 and sectioned by a second folding ruled line 54; an engagement piece 56 sectioned by a third folding ruled line 58 and extended at a distal end part of the display board; and an engagement part 56 formed at a distal end part of the engagement piece 56, widened in width from an opening part 62a to a deep part 62b, and engageable with the U-shape projecting piece 66.