Patent ID: 8647318

Claim:
An underpants-type disposable diaper, comprising an underpants-formed diaper main body, wherein said diaper main body comprises: an underpants-formed outer cover having a waist opening part extending in a lateral direction of the diaper main body and adapted to surround a wearer's trunk; and a pair of leg holes for the wearer's legs to pass through; the outer cover further including a front part to be positioned on a front side of the wearer and having two side edges opposite to each other in the lateral direction; a back part to be positioned on a back side of the wearer; and a crotch part joined to said front part and said back part and adapted to be positioned between the legs of the wearer; a substantially belt-shaped inner member directly joined to said outer cover on a skin-facing side of the diaper main body and having an absorbent body positioned between said leg holes; a plurality of waist bands formed of elastic material and extending along the waist opening part; elastic cords extending substantially straight in the front part and the back part, and parallel to the plurality of waist bands; and a group of elastic members positioned in the front part and the back part to form a continuous and substantially semicircular arc along each of the leg holes when viewed from a side of the diaper, wherein said group of elastic members in the front part has a first segment extending in the lateral direction from a corresponding one of the side edges of the front part and substantially parallel to a waist opening edge, and a second segment continuously extending in a curve from the first segment toward a center of the front part, the front part and the crotch part are separate pieces attached to each other at a joint portion, said group of elastic members has a first end adjacent to the joint portion and a second end adjacent to the corresponding side edge of the front part, and each of the elastic members is configured as a laterally elongated curve when said inner member is pulled in a direction around the wearer's trunk, wherein said group of the elastic members in the front part has a value X/Y, and the value X/Y is within a range of not less than 1.0 and not more than 3.0, where X is a minimum dimension in the lateral direction from the first end of the elastic members in the front part to the second end of the elastic members, and Y is a minimum dimension in a vertical direction perpendicular to the lateral direction from a lowermost end of the elastic members in the front part to an uppermost end of the elastic members.