The present invention provides a water purifying system capable of efficiently producing treated water containing boron at a low concentration. Water to be treated is first fed to the RO membrane apparatus 1 and the passed water is fed through the boron absorptive apparatus 2. Water which was passed through the boron absorptive apparatus 2 and of which boron was thus removed is fed through the electrodeionization apparatus 3. In this manner, water treated by electrodeionization is taken out as treated water. The condensed water of the electrodeionization apparatus 3 may be discharged or returned to the upstream side of the RO membrane apparatus 1 through a return pipe 4 so that the condensed water is added to water to be treated. Suitably used as the absorptive agent accommodated in the boron absorptive apparatus 2 is a boron selective absorptive agent capable of selectively absorbing boron.