The present invention is provided with sensor body (2) having a long plate shape, measurement part (3) provided in a front end section of sensor body (2), and connection terminal (4) provided in a rear end section of sensor body (2). Close contact prevention parts (10) having the same plate shape are provided in the same position of both a front surface and a back surface of sensor body (2), the position not overlapping with a position of a center of gravity of sensor body (2), measurement part (3), and connection terminal (4). A length in a longitudinal direction of sensor body (2) of close contact prevention parts (10) is shorter than a length thereof orthogonal to the longitudinal direction.