To obtain an unsealing structure wherein a lid of a carton can be simply and easily unsealed.

This carton comprises a lid sheet 2 on an upper part of an assembly-type carton, wherein a flap 6 provided on the lid sheet 2 is folded onto a rear surface of a front sheet 5 and perforated cuts 10, 10 are formed at both sides of the lid sheet 2. In this case, a first slit part 7 for hooking a finger is formed in the vicinity of the lid sheet 2 and the flap 6, a second semicircular slit part 8 is formed adjacent to the first slit part 7, and a foldable windowed piece 9 is formed inside the second slit part 8.