A magnetic separation device includes magnetic separation units in each of which a flow direction of raw water in a separation vessel is set to the same direction as a rotation direction of a magnetic drum. In the left-side magnetic separation unit, a raw water feeding channel is connected to the left side of the separation vessel, so that the raw water flows from left to right in the separation vessel and the treated water flows out of a discharge channel. The magnetic drum rotates in a counter clockwise direction. In the right-side magnetic separation unit, the raw water feeding channel is connected to the right side of the separation vessel, so that the raw water flows from right to left in the separation vessel and the treated water flows out of the discharge channel. The magnetic drum also rotates in the clockwise direction.