PROBLEM TO BE SOLVED: To provide a method of producing a group of particles of predetermined sizes in a controlled way.SOLUTION: A method of forming a particle comprises i) a step of dissolving a liquid substance 102 in a flow of a fluid 103 within a spray nozzle 101 in a flowing state, ii) a step of passing the resultant mixture through a spray outlet 109 of the nozzle in a spray form to put in a particle collection container 105 and iii) a step of separating and collecting particles into the container 105 by dissolving liquid matter in a liquid having a dissolving capability and using a fluid in a subcritical or supercritical state, with the fluid recycled in the process, and causing a make-up agent 107 which promotes formation of nucleus for the liquid matter and formation of the particles to be contained in the fluid.
