A disposable diaper for pets having a shortest straight line point being further on a stomach-side waist area side than a diaper center point, and comprising: a rear-side waist area; a stomach-side waist area; a crotch area; a flap section provided in the stomach-side waist area and having an end section in the rear-side direction; a diaper longitudinal direction center line; the diaper center point; a tail insertion opening; an absorbent core; an attachment section arranged in the flap section; an attachment section intermediate point; an attachment area that receives the attachment section; and the shortest straight line point being a point on the diaper longitudinal direction center line at the shortest direct distance, via a rear-side end section of the flap section in a straight line from the attachment section center point to the diaper longitudinal direction center line.