Abstract: A liquid filling method and in particular a lens material liquid filling method suitable for manufacturing a plastic lens. A thermal sensing portion (2a) of a temperature sensor (2) is set and kept to a temperature different from that of a liquid (3). The liquid (3) is poured into a vessel (8), a change of an output from the temperature sensor (2) is detected when the surface of the liquid (3) comes into contact with the thermal sensing portion (2a) by temperature detecting means (5), and control means (6) determines that the liquid surface has reached a desired level and sends a pouring stop command to a pouring mechanism (7) to complete the filling of the liquid.