The present invention provides a thin-film magnetic sensor including: a giant magnetoresistive film having a giant magnetoresistive effect, and thin-film yokes each composed of a soft magnetic material and electrically connected to both ends of the giant magnetoresistive film, in which each of the thin-film yokes includes an outer yoke which is composed of a first soft magnetic material and is provided outward with respect to the giant magnetoresistive film and an inner yoke which is composed of a second soft magnetic material and is provided between the giant magnetoresistive film and the outer yoke; the first soft magnetic material is composed of a crystalline or microcrystalline soft magnetic material; the thin-film magnetic sensor is obtained by (1) forming the each outer yoke, the giant magnetoresistive film and the each inner yoke in this order, and (2) performing a heat treatment for improving soft magnetic characteristics of the each outer yoke before forming the giant magnetoresistive film; and a length L2 of the each inner yoke satisfies the following equation (a) and equation (b): L2/t1≧1  (a) L2×100/(L1+L2)≦50  (b) where t1 is a thickness of the each outer yoke, and L1 is a length of the each outer yoke.