A stroke sensor has two magnets, which are magnetized in a cross-section direction and are displaced in a longitudinal direction, and two magnetism sensitive sections arranged parallel to the longitudinal direction. The magnets have circular-arc-shaped swelling end edges respectively and are magnetized such that the swelling end edges have opposite polarities. Thus, a distribution of a magnetic flux density on an arrangement axis substantially coincides with a sine curve. The magnetic flux having such the distribution is displaced in the longitudinal direction together with the magnets. The magnetism sensitive sections are arranged on the arrangement axis to be distant from each other by a distance of one fourth of a cycle of the sine curve. Thus, the stroke sensor that is not affected by temperature and that has high sensing accuracy can be provided.