NOVELTY - A photocurable composition comprises photocurable monomer (A), and carboxy group-containing monomer (B) or oligomer (I).    USE - Photocurable composition is used in apparatus e.g. flexible organic light-emitting device, lighting device, metal sensor pad, micro-disk laser, electrochromic device, photochromic device, micro-electro-mechanical system, solar cell, integrated circuit, charge-coupled device, light-emitting polymer device and light-emitting diode device (all claimed).    ADVANTAGE - The photocurable composition has low moisture permeability. The apparatus containing the photocurable composition contains sealing layer having high hardness, and has excellent deterioration-proof property.    DETAILED DESCRIPTION - A photocurable composition comprises photocurable monomer (A) and carboxy group-containing monomer (B) or oligomer of formula (I).    R3=H or 1-30C optionally substituted alkyl;    Y'=group of formula (ii)-(iv);    X1-X5=O, S, N-R or optionally substituted (R')C(R"), in which at least one being O, S, or N-R;    R,R',R"=H or optionally substituted 1-5C alkyl;    R1=1-30C alkylene, 1-30C alkyl, 1-30C alkyleneoxy, 1-30C alkylamine,1-30C alkylthio, 6-30C arylene, 7-30C aryl alkylene or 1-20C alkoxyl (all optionally substituted);    R2=H, or 1-30C alkyl, 1-30C alkyl ether, 1-30C alkylamine or dialkyl amine group, 1-30C alkylthio, 6-30C aryl, 7-30C arylalkyl or 1-20C alkoxy (all optionally substituted);    X6=O, S, or NR;    R4=1-30C alkyl, 1-30C alkyl ether, 1-30C alkylamine or dialkyl amine group, 1-30C alkylthio, 6-30C aryl, 7-30C arylalkyl or 1-20C alkoxy (all optionally substituted);    n=1-5;and    m=0 to n+1.    An INDEPENDENT CLAIM is included for apparatus (100), which has component (20) containing photocurable composition.    DESCRIPTION OF DRAWING(S) - The drawing shows sectional view of apparatus. (Drawing includes non-English language text)    Component (20)    Obstacle stack (30)    Inorganic barrier layer (31)    Organic barrier layer (32)    Apparatus (100)