Abstract: A strong pressure and a strong shearing force are exerted to a mixture, constituted of two kinds or more of powder materials including a drug powder, while causing the mixture to pass between a press section (26) of a press head (24) and a receiving surface (25) of a cylindrical rotator (23), thereby combining the drug powder with the other powder material. For example, at least one of a drug and a biocompatible polymer is made into a nano particle whose average particle diameter is less than 1000 nm, and the nano particle is made into a composite in accordance with a dry mechanical particle combining method, so as to form a polymer nano composite particle. Thus, it is possible to produce a composite particle, which contains a drug under a stable condition, in a short time, and it is possible to remarkably improve its handling property without losing advantages of the nano particle.