The present invention provides a color tone correcting agent having suitable heat resistance for use in an optical filter, a novel squarylium compound that is specifically preferable as the color tone correcting agent, and an optical filter including the color tone correcting agent. Specifically, the present invention provides a color tone correcting agent including a squarylium compound represented by the general formula (1), a novel squarylium compound which is represented by the general formula (4) and is preferable as the color tone correcting agent, and an optical filter including the color tone correcting agent. The general formula (1) and (4) are each as defined in the specification.