Pull-on disposable wearing article

A pull-on disposable wearing article having a waist-hole and a pair of leg-holes comprising;

• an absorbent batt structure;
• a chassis comprising:
• a longitudinal axis and a transverse axis being orthogonal to each other;
• a base sheet having:
• a front waist region made of a thermoplastic fibrous nonwoven fabric including a front waist band member adapted to be elastically extensible in a direction defined by said transverse axis but substantially not elastically extensible in a direction defined by said longitudinal axis,
• a rear waist region made of a thermoplastic fibrous nonwoven fabric including a rear waist band member adapted to be elastically extensible in a direction defined by said transverse axis but substantially not elastically extensible in a direction defined by said longitudinal axis, and
• a crotch region being substantially not elastically extensible at least in the direction defined by said longitudinal axis, side edges of said crotch region opposite to each other in the direction defined by said transverse axis describing curves concaved by a predetermined depth toward the longitudinal axis as viewed with said chassis as a whole developed with said front and rear waist regions unfolded away from each other;
• wherein said batt structure extends on an inner surface of said chassis between said front and rear waist regions,
• wherein the base sheet is substantially not elastically extensible in the direction defined by said longitudinal axis and said transverse axis,
• a first outer sheet and a second outer sheet being elastically extensible in the direction defined by said transverse direction and bonded to respective outer surfaces of said front and rear waist regions of said base sheet by a plurality of bonding lines extending continuously in the direction defined by said longitudinal axis while said first and second outer sheets being stretched in the direction defined by said transverse axis;
• wherein said base sheet is formed with a plurality of gathers along said plurality of said bonding lines in said front and rear waist regions as said first and second outer sheets contract, with said plurality of gathers defining channels which continuously extend in the direction defined by said longitudinal axis and are uniformly collapsed toward a predetermined side as viewed in the direction defined by said transverse axis;
• and
• a pair of liquid-resistant crotch side sheets, each having a proximal edge, a free edge and opposite ends and being elastically extensible in the direction defined by said longitudinal axis, having said proximal edges bonded to said crotch region along vicinities of bottoms of said concavely curving edges below side edges of said batt structure and said opposite ends bonded to said front and rear waist regions so that, when the article is put on the wearer's body, non-bonded zones of said crotch side sheets including said free edges are freely extensible/contractible with respect to said side edges of said batt structure and extend outward approximately from side edges of a liquid-absorbent zone of said batt structure corresponding to said side edges of said crotch region.