The invention provides a coating structure of a heat insulator for preventing powder falling of silica-aerogel in a composite sheet. The heat insulator includes: a composite layer having silica-aerogel enclosed in a nonwoven fabric; and a coating film containing a hydrophilic resin and a lipophilic resin and coating a surface of the composite layer. The nonwoven fabric resides in the coating film.In the coating film, the heat insulator includes the lipophilic resin which is present in the hydrophilic resin in the form of a plurality of islands.