To effectively eliminate sealing of gas and the air existing in an inserting strip by a simple method by providing at least one air bleeder, gas bleeder or an evacuating opening on the way of a conveying mixture to a place where both gears are engaged after an inserting passage.

A gear pump has two gears 1 supported to a casing 2 and engaged with one another. A mixture strip 19 of a rubber mixture plasticized in the pump and extruded under pressure is supplied to the gears 1 via an inserting passage 3. At this time, the air advanced into the pump is discovered on the way from a place 10 where the strip 19 is advanced to a place 4 where the gears 1 are engaged with one another or particularly at a ground between tooth gaps at the side of the gear 1. The air is arrived at the rubber mixture flowing out via an extruding opening 5 of the pump. To avoid it, an air bleeder or an evacuating passage 6 is provided in the casing 2.