PURPOSE: To provide an element having large nonlinear optical characteristics and excellent stability for a long time.

CONSTITUTION: This nonlinear optical thin film element consists of a three- dimensionally crosslinked resin partly consisting of α-cyanoacrylate deriv. group expressed by formula. Further, the dipole moment of the deriv. group is oriented in the film thickness direction. In formula, n is 0, 1, or 2, -Ar1- is an aromatic group of 5-14 carbon number, and R1- is an amino group expressed by R2R3N- or its halogenated hydrogen salt, ether group expressed by R4-O-, thioether group expressed by R5-S-, cyano group, ester group expressed by -COOR6 or -OCOR7, amide group expressed by -CONR8R9 or -NR10COR11, or hydrocarbon group expressed by -R12, R2-R12, are same or different univalent hydrocarbon groups of 1-8 carbon number or hydrogen atoms.