Disclosed is a device including a sensor configured to measuring an electrical characteristics of oil; a main body having the sensor in a sideward-facing orientation at one end of an elongated shape thereof; and a sensor cover having a base part configured to be attached to the main body; a tip head part having an arcuate shape or an annular shape being greater in size in a radial direction with respect to the sensor, disposed in a manner protruding at a tip side of the main body with respect to the sensor; and a connection part including a first connecting pillar connecting the base part and the tip head part and a second connecting pillar having a width smaller than a width the first connecting pillar.