To provide a linear displacement sensor capable of acquiring output voltage proportional to the displacement from the hole IC if a pair of bar permanent magnets are moved to the fixed hole IC.

The pair of bar permanent magnets 3, 3' are held on the movable member 4 opposite to each other with a noncontact state across the hole IC 2 which is fixed to the fixing member 1. When the bar permanent magnets 3, 3' are moved to left and right, from the hole IC 2 the output voltage varying linearly is obtained, by characteristically providing the rectangular ferromagnetic plate 5, the width of which becomes smaller according to reach the midpoint 5a than the widths of both the ends gradually on the pair of bar permanent magnets 3, 3', at least one of longitudinally directional faces 3a, 3a' opposing to each other, so as to obtain the output voltage varying linearly from the hole IC.