The present invention provides a filtration device combined with self-priming pump in which a filter replacement work is easy and safe, and removal of air inside of a pump and priming are not necessary. And this filtration device is characterized to provide with a pump unit, which is a valveless-construction self-priming pump without a check valve, including a suction port, a suction chamber, an impeller, a self-priming chamber, a discharge port from an upstream of a channel to a downstream thereof in this order, the suction port and the discharge port being arranged above the level of the suction chamber and the impeller, and a self-priming chamber arranged above the level of the suction port and the discharge port; a filtration unit arranged on a channel between the self-priming chamber and the discharge port and above the level of the self-priming chamber; and a filter arranged inside of the filtration unit and above the level of residual liquid inside of the pump unit at the time of suspending of the pump unit.