An antisense molecule which acts on both directions of the inhibition and expression of a gene function and is capable of on-off switching of a gene function appropriately depending on the external factors (orientation controlling factors); and a method for reversibly controlling the expression of a gene function by using the antisense molecule. Such an antisense molecule, which has at least one sugar-base moiety consisting of sugar and a purine or pyrimidine base bonded thereto via a glucoside bond, can bind to a mRNA/gene and/or dissociate therefrom under the orientation control of the base moiety in the molecule by the orientation controlling factors.