PURPOSE:To obtain a plant growth regulator showing exceeding growth and development properties for the use in object of growth promoting and giving strong plant body for the use in object of growth depressing, containing specific a norditerpene-based compound extracted and isolated from nagi podocarpus as a plant of Podocarpaceae as an active ingredient. CONSTITUTION:The norditerpene-based compound expressed by formula I (R<1>-R<3> is H or hydroxyl; R<1> and R<2>, or R<2> and R<3> are epoxy respectively bonded with each other) which is readily isolatable from a seed endosperm or root skin, etc., of nagi podocarpus (e.g., nagilactone F expressed by formula II) is contained in the aimed plant growth regulator as an active ingredient. Growth promoting effect such as improvement of germinating properties of the seed or enlarging of the seed leaf area is obtained in case of treatment of said plant growth regulator with relatively small amount of the drug, on the other hand, a strong plant body is obtained by manifestation of depression effect in case of treatment with relatively large amount of the drug. Said regulator is effective for the whole plant, especially effective for plants of Solanaceae, Cruciferae and Gramineae, etc., further suitable for treatment of the plant seed.
