A fluid handling unit 16 has an outside large-diameter cylindrical portion 16a, an outside small-diameter cylindrical portion 16b and an inside cylindrical portion 16c, which are integral-molded so as to be integrated with each other. The inside cylindrical portion 16c has a plurality of slits 16d, which are extend from the lower end of the inside cylindrical portion 16c to the upper end thereof, for establishing a communication between an inside fluid housing chamber 30, which is formed in the inside cylindrical portion 16c, and an outside fluid housing chamber 28 which is formed between the inside cylindrical portion 16c and the outside small-diameter cylindrical portion 16b. The plurality of slits 16d are designed to cause the most part of a liquid in the inside fluid housing chamber 30 to enter the outside fluid housing chamber 28 due to capillarity when the quantity of the liquid fed into the fluid handling unit 16 is not larger than a predetermined quantity, and to allow the liquid in the outside fluid housing chamber 28 to enter the inside fluid housing chamber when the quantity of the liquid fed into the fluid handling unit 16 exceeds the predetermined quantity.