A magnetic flux detection unit and a rectangular solid magnet are provided. The magnetic flux detection unit includes one or more pairs of Hall sensors, each pair having two Hall sensors arranged on a substrate. The solid magnet is arranged movably in a direction in a plane parallel to the substrate. Each pair of two Hall sensors is arranged on the substrate so that a line connecting the centers of magnetism sensing sections of each pair of two Hall sensors is orthogonal to a movement direction of the magnet. A tetragon has a long side and a short side and the long side has a inclination angle to the line connecting the centers of magnetism sensing sections of the each pair of two Hall sensors. The magnet has one N-pole and one S-pole separately magnetized in orthogonal to the substrate on which the Hall sensors are arranged.