PURPOSE: To prevent a high-melting component from coagulating, by making the temperature of mixed liquid higher than the melting point of a liquid at a high-temperature side at the first blending part, and carrying out blending at the second blending part in a state where the high-melting component is diluted.

CONSTITUTION: The line 1 of a liquid (the liquid C) at low-temperature side is provided with the first blending part A to blend it with a liquid (the liquid H) at high-temperature side, the by-pass line 2 which by-passes the blending part A and makes the liquid C flow partially if formed, and the second blending part B to join the line 2 and the line 1 is made. A flow rate of the liquid C to flow in the line 1 is reduced by the line 2, and the blending is carried out at the blending part A in such a way that the temperature of the blended liquid is higher than the melting point of the liquid H. In the concrete constitution of the blending parts A and B, junction pipe method, spray chip method, obstacle collision method, inserted tube method, etc. may be used.