An object is to improve the waterproof and antifouling properties of a device for measuring the amount of water in a subjects body. A device (100) for measuring the amount of water in a subjects body according to the present invention includes a main body part (110) formed in a linear shape and an insertion part (120) extending in a curved shape from one end of the main body part (100). The insertion part (120) includes a tip side insertion part (120-2) having a tip surface (122) to which a sensor unit (121) is fixed, wherein the sensor unit (121) is brought into contact with a body surface of a subject to measure data regarding water in a subjects body, a base end insertion part (120-1) supporting the tip side insertion part (120-2) through a slide mechanism, wherein the slide mechanism allows the tip side insertion part (120-2) to slide in a direction substantially perpendicular to the tip surface (122), and a protective member (651) liquid-tightly covering the slide mechanism between the tip side insertion part (120-2) and the base end side insertion part (120-1), wherein the protective member (651) smoothly connects the outer peripheral surface of the tip side insertion part (120-2) and the outer peripheral surface of the base end side insertion part (120-1) to each other .
