A thermal bonding conjugate fiber constituted from a first component comprising a polyester resin and a second component comprising a polyolefin resin with a melting point lower than that of the polyester resin by not less than 20° C., characterized in that a post-heat treatment bulk retention rate thereof is 20% or more when calculated by the following measurement method: Bulk retention rate=(H1 (mm)/H0 (mm))×100(%) (wherein H0 is the web height when a 0.1 g/cm2 load is applied to a web with a mass per unit area of 200 g/m2; and H1 is the web height after a heat treatment for 5 min at 145° C. when a 0.1 g/cm2 load is applied to that web).