A filter medium includes: a porous substrate; a nanofiber web laminated on both surfaces of the porous substrate, the nanofiber web being formed of accumulated nanofibers made of a polymer material and having a number of fine pores; and a fuse reinforcement material interposed between the nanofiber web and the porous substrate for adhesion with the nanofiber web and the porous substrate integrally. The porous substrate is surrounded by the nanofiber web except for an upper edge of the porous substrate, the upper edge of the porous substrate protrudes with respect to the nanofiber web to form a protruding portion, and the protruding portion is configured to be connected with a discharge hole through which purified water via the porous substrate is discharged.