A displacement detection unit includes a magnet and a magnetic detector. The magnet includes a first magnetic-pole region polarized into a south pole and a second magnetic-pole region polarized into a north pole, and generates a magnetic field around the magnet. The magnetic detector is movable relative to the magnet in a first direction, and detects a change in the magnetic field and thereby detects a displacement of the magnet in the first direction. The magnet includes a transition section in which a ratio of a magnetic volume of the second magnetic-pole region in a second direction to a magnetic volume of the first magnetic-pole region in the second direction gradually varies in the first direction. The second direction is orthogonal to the first direction.