The present invention provides a composition in which a fungicidal effect against a cultivated crop infected by a plant disease is stable and highly active. An excellent agricultural or horticultural fungicide composition for controlling a plant disease is provided by using (a) at least one imidazole compound represented by formula (I): wherein R represents a C1-6 alkyl group or a C1-6 alkoxy group; and n represents an integer of 1 to 5 and (b) polyoxins as active ingredients; by combination as compared to a single use of each compound, and a plant disease is thereby controlled.