A disposable male adult pull-on diaper having a lateral direction, a longitudinal direction and a center line extending in the lateral direction and including a lower torso cover which assumes a tubular shape and defines a front waist region, a back waist region and a crotch region, an absorbent chassis provided with an absorbent structure and extending between the front waist region and the back waist region and having a front end portion and a back end portion adapted to overlap the front waist region and the back waist region, respectively; the lower torso cover has front and back elastic regions defined by a plurality of front and back waist elastic elements (21, 22) in which the front and back elastic elements (21, 22) extend in the lateral direction of the lower torso cover and are contractibly secured thereto under tension, and front inelastic regions in a front portion of the crotch region defined between the center line and the front waist region and in a portion of the front waist region adjacent to the crotch region, the inelastic regions including none of the elastic elements extending in the lateral direction; the absorbent chassis is constituted by an absorbent body formed of a core included in the absorbent structure, a liquid-permeable bodyside liner and a liquid-impermeable backsheet and a cover sheet to wrap the absorbent body, including an extension formed by the bodyside liner and the backsheet extending outward in the longitudinal direction beyond the core and a waist opening and a pair of leg-openings; the diaper is characterized in that: the front end portion of the absorbent chassis has a front end portion that is the extension of the bodyside liner and the backsheet and joined to the lower torso cover in the front elastic region, a front end adjoining portion not joined to the lower torso cover in the front elastic region and extending adjacent to the front end portion on the side of the crotch region, except both laterals of the front end adjoining portion that are opposite to each other in the lateral direction of the lower torso cover and partially joined to the lower torso cover in the elastic region, the absorbent body extends at least from the crotch region to the front end adjoining portion, and a front area of the absorbent chassis extending adjacent to the front end adjoining portion on the side of the crotch region is joined to the lower torso cover in the inelastic region of the front portion extending adjacent to the front end adjoining portion on the side of the crotch region. the lower torso cover has front and back elastic regions defined by a plurality of front and back waist elastic elements (21, 22) in which the front and back elastic elements (21, 22) extend in the lateral direction of the lower torso cover and are contractibly secured thereto under tension, and front inelastic regions in a front portion of the crotch region defined between the center line and the front waist region and in a portion of the front waist region adjacent to the crotch region, the inelastic regions including none of the elastic elements extending in the lateral direction; the absorbent chassis is constituted by an absorbent body formed of a core included in the absorbent structure, a liquid-permeable bodyside liner and a liquid-impermeable backsheet and a cover sheet to wrap the absorbent body, including an extension formed by the bodyside liner and the backsheet extending outward in the longitudinal direction beyond the core and a waist opening and a pair of leg-openings; the diaper is characterized in that: the front end portion of the absorbent chassis has a front end portion that is the extension of the bodyside liner and the backsheet and joined to the lower torso cover in the front elastic region, a front end adjoining portion not joined to the lower torso cover in the front elastic region and extending adjacent to the front end portion on the side of the crotch region, except both laterals of the front end adjoining portion that are opposite to each other in the lateral direction of the lower torso cover and partially joined to the lower torso cover in the elastic region, the absorbent body extends at least from the crotch region to the front end adjoining portion, and a front area of the absorbent chassis extending adjacent to the front end adjoining portion on the side of the crotch region is joined to the lower torso cover in the inelastic region of the front portion extending adjacent to the front end adjoining portion on the side of the crotch region. the front end portion of the absorbent chassis has a front end portion that is the extension of the bodyside liner and the backsheet and joined to the lower torso cover in the front elastic region, a front end adjoining portion not joined to the lower torso cover in the front elastic region and extending adjacent to the front end portion on the side of the crotch region, except both laterals of the front end adjoining portion that are opposite to each other in the lateral direction of the lower torso cover and partially joined to the lower torso cover in the elastic region, the absorbent body extends at least from the crotch region to the front end adjoining portion, and a front area of the absorbent chassis extending adjacent to the front end adjoining portion on the side of the crotch region is joined to the lower torso cover in the inelastic region of the front portion extending adjacent to the front end adjoining portion on the side of the crotch region.