A method of casting a plastic lens starting material liquid using a casting apparatus comprising at least a mixing and discharging part and a casting part, and casting a plastic lens starting material liquid sequentially into multiple casting molds. Discharge of the plastic lens starting material liquid from the mixing and discharging part is halted based on a discharge halt preparation completion signal transmitted by the casting part, the discharge that has been halted is recommenced (1) at least based on a discharge recommencement preparation completion signal transmitted by the casting part or (2) by reception by the mixing and discharging part of a forced discharge start signal transmitted upon elapsing a predetermined time following halting of the discharge or following reception of the discharge halt preparation completion signal without transmission of a discharge recommencement preparation completion signal by the casting part, and the stirring in the mixing and discharging part is continued during the period when the discharge is halted.