NOVELTY - A nitrogen-containing condensed ring compound having aromatic ring-containing structural unit (I) or (II) is new.    USE - Nitrogen-containing condensed ring compound is used for nitrogen-containing condensed-ring polymer for organic thin film for organic thin film element, organic thin-film transistor and organic solar cell (all claimed).    ADVANTAGE - The nitrogen-containing condensed compound has excellent solubility with respect to organic solvent and excellent electron transport characteristics.    DETAILED DESCRIPTION - A nitrogen-containing condensed ring compound having aromatic ring-containing structural unit of formula (I) or (II) is new.    Ar1=4C or more optionally substituted aromatic ring;    one of Y1 or Y2=single bond, other is group of formula: -C(=X1)- or -C(R11)(R12)-;    one of Y3 or Y4=single bond, and other is group of formula: -C(=X2)- or -C(R21)(R22)-, at least 1 of Y1-Y4 is group of formula: -C(R11)(R12)- or -C(R21)(R22)-;    R11,R12,R21,R22=H, halo, cyano or monovalent group containing alkane structure, at least one of R11 and R12 and/or at least one of R21 and R22 are monovalent group containing alkane structure;    X1,X2=oxygen atom, sulfur atom, or =C(A)2;    A=H, halo, or monovalent group;    W1,W2=-N= or -C(R00)-, at least one of W1 and W2 is group of formula: -N=;    R00=A;    Z1,Z2=-O-, -S-, -Se-, -Te-, -S(=O)-, -S(=O)(=O)-, -C(-R3)=C(-R4)-, -C(-R5)=N-, or -N(-R6)-;    R3-R6=H, halo, or monovalent group;and    R3+R4+C=ring.    INDEPENDENT CLAIMS are included for the following:    (1) nitrogen-containing condensed-ring polymer, which has two or more structural units (I) or (II); and    (2) organic thin film, which contains the nitrogen-containing condensed ring compound and/or nitrogen-containing condensed-ring polymer.    DESCRIPTION OF DRAWING(S) - The drawing shows the schematic cross-sectional view of organic thin-film transistor.    Substrate (1)    Active layer (2)    Insulating layer (3)    Gate electrode (4)    Organic thin-film transistor (100)