Abstract: An apparatus, a method, and a program for visualizing a Boolean expression so that it is readily recognized what is added to or excluded from conditions. A Boolean expression to be visualized is input in the form of a binary tree in which a leaf node represents an operand in the Boolean expression and a node other than the leaf node represents an operator in the Boolean expression. The input binary tree is transformed into a two-dimensional nested representation composed of a plurality of regions, and a pictorial representation for visualization is drawn on the basis of the nested representation and is displayed. When the Boolean expression is provided in a string expression, the string expression is transformed into a binary tree.