There are provided an effect enhancer for an agricultural chemical and an a chemical formulation which is not pharmaceutically harmful to various crops and can be safely used and which has an excellent effect enhancing function to various agricultural chemicals. The effect enhancer for the agricultural chemical comprises, as an effective component, a compound represented by the following formula (I): R—O[(EO)x(PO)y](EO)z—H, wherein EO is an oxyethylene group; PO is an oxypropylene group; R is a straight-chin or branched alkyl group or alkenyl group having 6 to 30 carbon atoms; x is a value of 1 to 30 on the average; y is a value of 1 to 30 on the average, and z is a value of 1 to 30 on the average. The agricultural chemical formulation composes the above-mentioned surfactant and a technical grade of active ingredient or an active compound for an agricultural chemical.