To provide a method for synthesizing monoterpenes from an allyl alcohol compound in a short time, without addition of a catalyst, and to provide an apparatus for the same.

This method for producing the monoterpenes comprises synthesizing the monoterpenes from the allyl alcohol compound by using a subcritical or supercritical fluid as a reaction solvent, without the addition of the catalyst. Further, the apparatus for producing the same is provided. Thus, the monoterpenes which are useful as a raw material for a perfume and a raw material for a pharmaceutical are efficiently mass-produced in a short time. An initial cost of a process is reduced, and further a running cost thereof is reduced, because of not using the catalyst. Further, production harmonious with the environment is realized.