The present invention provides a primer for footwear constituting members, wherein the primer includes an acid-modified polyolefin resin and a medium; the acid-modified polyolefin resin is a copolymer including an olefin unit and an unsaturated carboxylic acid unit; the copolymer includes as the olefin unit, a propylene unit (A) and an olefin unit (B) other than the propylene unit; the mass ratio (A/B) between the propylene unit (A) and the olefin unit (B) other than the propylene unit is 60/40 to 95/5; and the content of the unsaturated carboxylic acid unit is 0.1 to 10 parts by mass in relation to 100 parts by mass of the total amount of (A) and (B).