A heat insulator includes a foamed glass body, and a hollow member that stores the foamed glass body in a hollow portion. The foamed glass body is composed of a silicate glass material containing R2O compounds and RO compounds. In a case that a value A is a weight ratio (%) of the R2O compounds in terms of oxides to the whole, and a value B is a weight ratio (%) of the RO compounds in terms of oxides to the whole, an absolute value of a value C obtained by an expression of value A−2.08×value B is 5.27 or less, or an absolute value of a value D obtained by an expression of value A−2.68×value B is 3.23 or less.