NOVELTY - A silicon-containing curable composition contains (in parts mass) silicon-containing polymer (100) obtained by hydrolytically condensating organosilane mixture containing organosilane (I) (5-50 mol%), organosilane (II) (0-50 mol%), organosilane (III) (0-40 mol%) and organosilane (IV) (0-50 mol%), prepolymer (0-200) obtained by hydrosilylation reaction of cyclosiloxane copolymer (X) and alkene-containing compound (XI) or 1,2,4-trivinylcyclohexane, cyclosiloxane compound (0-30), organic peroxide (0.0001-10) and/or metal catalyst (0-1) and filler (10-1500).    USE - Silicon-containing curable composition is used for hardened material, and lead frame substrate for light-emitting element used for light-emitting-diode-type light-emitting apparatus (all claimed). Uses include but are not limited to tube, sealing material, contact lens, gasket, machine component, motor-vehicle component, lining, optical machine, solar cell and heat-dissipation material.    ADVANTAGE - The silicon-containing curable composition has excellent hardenability. The hardened material containing the silicon-containing curable composition has excellent heat resistance, light resistance, crack resistance and mechanical strength.    DETAILED DESCRIPTION - A silicon-containing curable composition contains (in parts mass) silicon-containing polymer (100) obtained by hydrolytically condensating organosilane mixture containing organosilane of formula: R1SiX3 (I) (5-50 mol%), organosilane of formula: R2SiX3 (II) (0-50 mol%), organosilane of formula: R3R4SiX2 (III) (0-40 mol%) and organosilane of formula: R5SiX3 (IV) (0-50 mol%), and having weight average molecular weight of 3000-100000, prepolymer (0-200) obtained by hydrosilylation reaction of cyclosiloxane copolymer (X) and alkene-containing compound (XI) or 1,2,4-trivinylcyclohexane and having 2 or more silane groups in a molecule, cyclosiloxane compound (0-30) having 2 or more carbon-carbon double bonds with reactivity with respect to silane in a molecule, organic peroxide (0.0001-10) and/or metal catalyst (0-1) and filler (10-1500).    R1=2-6C alkenyl;    R2=1-6C alkyl;    R3,R4=1-6C alkyl, 2-6C alkenyl, or phenyl optionally substituted by 1-6C alkyl;    R5=phenyl optionally substituted by 1-6C alkyl;    X=hydroxy, 1-6C alkoxy, or halo;    R6-R8=1-6C alkyl, or phenyl optionally substituted by 1-6C alkyl;    f=2-10;    g=0-8;    f+g=2 or more;and    n=1 or 2.    At least one of R2-R4 is methyl. INDEPENDENT CLAIMS are included for the following:    (1) hardened material; and    (2) lead frame substrate (10).    DESCRIPTION OF DRAWING(S) - The drawing shows the schematic view of the lead frame substrate.    Lead frame substrate (10)    Resin molding (11)    Recessed portion (12)    Pad portion surface (13a)    Lead frame (50)