A β-1,3-glucanase that exhibits decomposition activity with respect to paramylon derived from the genus Euglena. The β-1,3-glucanase is derived from the genus Euglena and exhibits the properties indicated below: (1) effect: hydrolyzing the β-1,3-bond of β-1,3-glucan; and (2) substrate specificity: decomposing at least paramylon. The β-1,3-glucanase additionally exhibits the properties indicated below: (3) decomposition activity: the ratio of paramylon decomposition activity with respect to laminarin decomposition activity is 20% or higher; (4) optimum pH: 3.7-7.0; and (5) optimum temperature: 30-70° C.