This thermally decomposable binder includes an aliphatic polycarbonate resin including structural units represented by formula (1) (in the formula, R1, R2, and R3 each represent hydrogen, a C1-10 alkyl group, or a C6-20 aryl group, and may be the same or different, and n is 1 or 2). An inorganic fine particle dispersion paste composition and this thermally decomposable binder including the aliphatic polycarbonate resin can be used as an optical material for general moulded articles, films, fibres, optical fibres, optical disks, and the like, a thermally decomposable material for ceramic binders, lost-foam castings, and the like, a medical material for drug capsules and the like, an additive for a biodegradable resin, and a main component of a biodegradable resin.