Disk filter and filter disk used for same

A disk filter comprising:

• a filter case including an inlet and an outlet for liquid;
• an elongated center shaft disposed in the filter case;
• and
• a plurality of filter disks detachably housed in the filter case, the filter disks each having an annular plate shape and a predetermined thickness, wherein
• the filter disks are stacked on one another, with the center shaft inserted in a hole of each of the filter disks,
• each filter disk includes
• a plurality of grooves that connect an outer periphery and an inner periphery of the filter disk and define a liquid channel, the grooves being provided on at least one of a front surface and a rear surface of the filter disk at a predetermined interval in a circumferential direction of the filter disk,
• each groove is defined in a curved shape whose curvature gradually increases from the outer periphery toward the inner periphery, and
• a width of an opening of each groove in the circumferential direction at the outer periphery is greater than a width of an opening of the groove in the circumferential direction at the inner periphery.