MOISTURE SENSOR AND STEERING SYSTEM

A moisture sensor that consumes reduced power is provided, and a steering system with the moisture sensor is also provided. A recessed portion (17c) is formed in an inner wall surface of a lower portion of a reduction gear housing (17b) (a lower wall surface in FIG. 2) in the direction of gravity and between a bearing (44) and an outer wall of the reduction gear housing (17b) (a right side wall in FIG. 2). The recessed portion (17c) is formed to have such a depth that the recessed portion (17c) does not penetrate the reduction gear housing (17b). The recessed portion (17c) is formed in the reduction gear housing (17b) within a given range in a circumferential direction with respect to the axis of a rack shaft (12) serving as the center. A moisture sensor (60) is mounted in the recessed portion (17c) to detect water infiltrating into a housing (17). The moisture sensor (60) has a transmission circuit that operates using a water battery as a power supply source. The water battery generates power when water flows into the water battery.