The present invention provides a method of increasing production of amorpha-4,11-diene and a method of increasing production of natural rubber. The present invention relates to a method of increasing production of amorpha-4,11-diene which includes the step of attaching an enzyme inhibitor to Arabidopsis thaliana into which has been introduced a gene encoding amorphadiene synthase. The enzyme inhibitor inhibits at least one enzyme other than amorphadiene synthase, that catalyzes an enzymatic reaction in which farnesyl diphosphate acts as a substrate. The present invention also relates to a method of increasing production of natural rubber which includes the step of attaching an enzyme inhibitor to a rubber-producing plant. The enzyme inhibitor inhibits at least one enzyme other than enzymes involved in natural rubber synthesis, that catalyzes an enzymatic reaction in which farnesyl diphosphate acts as a substrate.