PROBLEM TO BE SOLVED: To provide an open type disposable diaper fitted to the buttocks of a wearer and having an appearance like underwear.SOLUTION: The open type disposable diaper includes a front waist area, a back waist area, a crotch area positioned between the front and back waist areas, an elastic waist belt extending laterally, and an absorption chassis extending in the front/back direction. The open type disposable diaper further includes a pair of buttock cover parts interposed between lateral front end edges of the elastic waist belt and both front/back-directional side edges of the absorption chassis, and outline edges of the buttock cover parts diagonally extend from the front end edges of the elastic waist belts positioned in the back waist area to the side edges of the absorption chassis positioned in the crotch area.
