A floor reaction force to a foot of a legged mobile robot is detected with a suitable degree of accuracy, by use of a strain sensor having comparatively low sensitivity. The foot includes an upper frame connected to a movable leg, a lower frame which is disposed under the upper frame and contacts with a walking surface, a strain generating member which is connected to the upper frame and the lower frame at different positions from each other in top plan view and undergoes bending deformation according to a change in distance or inclination between the instep member and the sole member, and a plurality of strain sensors disposed at positions different from each other on the strain generating member.