Moisture meter configured to be held by an armpit of a subject and to measure the amount of water of the subject by being in contact with a skin surface of the armpit It comprises a main body unit (110) formed in a linear shape, a sensor unit (121) which is configured to measure data relating to moisture inside a living body by being in contact with a body surface of a subject and an insertion unit (120) which holds the sensor unit at its distal surface slidably toward a direction approximately perpendicular to the distal surface and also which outputs a signal for instructing the measurement-start of the sensor unit by detecting the slide of the sensor unit, wherein for the housing of the insertion unit, the distal surface is formed such that the angle formed between the longitudinal direction of the main body unit and the slide direction of the sensor unit becomes approximately 20° to 45°, and also, is formed so as to go along the slide direction in the vicinity of the distal surface.
