A liquid coolant supply pipe (23) and an over flow pipe (24) are provided on the outer side of a capsule forming pipe (3) through which a liquid coolant (12) flows and into which liquid droplets (13) are dropped from a nozzle (2). The liquid coolant (12) is supplied to the liquid coolant supply pipe (23) by a low pulsatory motion type pump such as a rotary pump. The flow of the liquid coolant (12) is regulated by a flow straightening block (26) provided in the liquid coolant supply pipe (23), passes through a liquid coolant introducing section (31) having a curved surface, and then flows into the capsule forming pipe (3) from an upper portion opening (34) in a cap (29) mounted to the upper part of the capsule forming pipe. The liquid coolant (12) flows into the capsule forming pipe (3) and the excess of the liquid coolant (12) flows into the overflow pipe (24) from the entire periphery of the liquid coolant supply pipe (23).
