A resin composition for sealing an electronic device and other things being capable of sealing an electronic device without trapping air and being capable of suppressing the permeation of water vapor is provided. The present invention includes a polybutadiene polymer represented by chemical formula (1) and having a (meth) acryloyl group at a terminal end; and a photopolymerization initiator, and does not include a thermoplastic resin having a mass-average molecular weight of 50,000 or more: wherein R1 and R2 each represent a hydroxyl group or H2C═C(R7)—COO—; R3 and R4 each represent a C1-C16 substituted or unsubstituted, non-N-containing divalent organic group; R5, R6 and R7 each represent a hydrogen atom or a C1-C10 alkyl group; l and m each represent 0 or 1; n represents an integer from 15 to 150; and x:y=0 to 100:100 to 0; R1 and R2 are never both a hydroxyl group.