We have developed a new facile and continuous method for production of 5-hydroxymethylfurfural (HMF) which is expected to have beneficial effects on the prevention of life-style related diseases such as hypertension and diabetes. HMF is made from inexpensive saccharides such as glucose, in high-pressure and high-temperature water medium. The system enables rapid heating from room temperature to 400 °C within a very short time (less than 0.01 s) by mixing high-pressure and high-temperature water and an aqueous solution of saccharide in a microreactor (micromixer). The reaction method with rapid heating and cooling achieves the production of HMF in high yield (70 %) and high selectivity (80 %).