Rear wheel steering device

A rear wheel steering device comprising:

• a drive unit that is provided in a housing;
• a rod that is provided in the housing and reciprocates along an axis of the rod in a non-rotating state by the drive unit;
• and
• a displacement detecting unit that is provided in the housing and detects displacement of the rod,
• the displacement detecting unit including
• a magnet that is fixed to the rod and reciprocates together with the rod,
• a pair of elements that are dispersedly arranged along the axis and are arranged in a state in which ranges in which strength of a magnetic field formed by the magnet is detected overlap with each other, and
• a control unit that calculates a position of the magnet along the axis with respect to the pair of elements from a detection result obtained by at least one of the pair of elements,
• wherein when a distance between an end portion of one of the pair of elements and an end portion of another of the pair of elements, the end portions farthest from each other among combinations of end portions of the pair of elements, is defined as an inter-element distance, a length of the magnet along the axis is shorter than the inter-element distance.