A device for measuring the pollution index of a filtration membrane, the device comprising: a raw water supply part supplying raw water to be measured; a first filtration membrane; a raw water supply line connecting the raw water supply part to the first filtration membrane; a first flow rate measuring part measuring the flow rate; a first path line connecting the first filtration membrane to the first flow rate measuring part; a second path line connected to the first path line in parallel; a second filtration membrane installed in the second path line and having a filtration characteristic different from the first filtration membrane; a first path selection valve installed in the first path line in parallel with respect to the second filtration membrane so that a first measuring path through which the raw water flows from the raw water supply part to the first flow rate measuring part passes through the first filtration membrane and a second measuring path through which the raw water flows from the raw water supply part to the first flow rate measuring part successively passes through the first filtration membrane and the second filtration membrane; and a pollution index measuring part measuring the pollution indexes of the first filtration membrane and the second filtration membrane on the basis of the flow rate measured by the first flow rate measuring part with respect to the first measuring path and the second measuring path, wherein, when the first path selection valve is opened, the pollution index measuring part is configured to measure the pollution index of the first filtration membrane by measuring the flow rate of water filtered through the first filtration membrane alone via the first measuring path, and, when the first path selection valve is closed, the pollution index measuring part is configured to measure the pollution index of the second filtration membrane by measuring the flow rate of water sequentially filtered through the first filtration membrane and the second filtration membrane along the second measuring path. a raw water supply part supplying raw water to be measured; a first filtration membrane; a raw water supply line connecting the raw water supply part to the first filtration membrane; a first flow rate measuring part measuring the flow rate; a first path line connecting the first filtration membrane to the first flow rate measuring part; a second path line connected to the first path line in parallel; a second filtration membrane installed in the second path line and having a filtration characteristic different from the first filtration membrane; a first path selection valve installed in the first path line in parallel with respect to the second filtration membrane so that a first measuring path through which the raw water flows from the raw water supply part to the first flow rate measuring part passes through the first filtration membrane and a second measuring path through which the raw water flows from the raw water supply part to the first flow rate measuring part successively passes through the first filtration membrane and the second filtration membrane; and a pollution index measuring part measuring the pollution indexes of the first filtration membrane and the second filtration membrane on the basis of the flow rate measured by the first flow rate measuring part with respect to the first measuring path and the second measuring path, wherein, when the first path selection valve is opened, the pollution index measuring part is configured to measure the pollution index of the first filtration membrane by measuring the flow rate of water filtered through the first filtration membrane alone via the first measuring path, and, when the first path selection valve is closed, the pollution index measuring part is configured to measure the pollution index of the second filtration membrane by measuring the flow rate of water sequentially filtered through the first filtration membrane and the second filtration membrane along the second measuring path.