To provide a leukocyte removing device and a leukocyte removing method for removing leukocyte in blood in such a manner that while the function of an anticoagulant is maintained, the risk for the rising of a pressure loss of a leukocyte removing filter is reduced by reducing the clogging of blood components or the risk for the coagulation, and the blood of a target amount is processed.

A blood inlet, the leukocyte removing filter and a blood returning port are connected in this order by an excretory duct, and an excretory duct for injecting the anticoagulant is provided on the upstream side excretory duct of the leukocyte removing filter for this leukocyte removing device. In the leukocyte removing device, a cooling means for cooling the blood to be at a temperature from 10°C to lower than 30°C is provided on the leukocyte removing filter and/or on the upstream side excretory duct for the leukocyte removing device.