PURPOSE: To improve heat exchanging efficiency by providing a heat medium tank for enclosing a chemical storage tank, and employing the storage tank as one type of heat exchanger having large heat transfer surface area.

CONSTITUTION: A chemical supply port 8a is provided in a chemical storage tank 1 through the upper wall of a heat medium tank 4, and a heat medium liquid supply port 3 and a chemical discharge port 9 are provided at the lower part. The tank 1 is mounted in the tank 4, a heat medium liquid supply port 10a is formed at the upper part, and a chemical discharge port 8b and a heat medium liquid discharge port 10b connected to the tank 1 are provided at the lower part. A heat exchanger 2 is attached into the tank 1. One end of the exchanger 2 is connected to the port 3, and the other end is connected to the port 10b of the tank 4 connected to the tank 1. The exchanger 5 is attached into the tank 4, its one end is connected to the port 9 of the tank 1, and the other end is connected to the port 8b of the tank 4.