A constant force generator includes a case of a tube-shaped ferromagnetic material and extending in an axial direction, a tube-shaped stator disposed in the case, and a rod-shaped shaft disposed in the tube-shaped stator via a gap. The tube-shaped stator includes N main permanent magnets magnetized in a radial direction and disposed adjacently at regular angular intervals of (360/N) degrees, and an even number of secondary permanent magnets magnetized in a circumferential direction and sandwiching each of the N main permanent magnets on both sides in the circumferential direction. The secondary permanent magnets sandwich the both sides of each main permanent magnet so that magnetic poles of the secondary permanent magnets, facing the both sides of the sandwiched main permanent magnet, have a polarity the same as an inside magnetic pole of the sandwiched main permanent magnet. The rod-shaped shaft at least includes a shaft portion of a magnetic material.