Provided is a water absorbent sheet retaining mat which can retain a water absorbent sheet easily and surely. A water absorbent sheet retaining mat M for retaining a water absorbent sheet Sa having a first polygonal contour, comprises: a mat member Pm having a second polygonal contour defined by mutually opposing a first main plane St and a second main plane Sb and at least one retaining member Pr having a slit member S comprised of at least one slit formed in a top surface Sru at a predetermined height from the first main plane for accepting a part of perimeter of the water absorbent sheet being inserted therein, wherein the water absorbent sheet is laid on the first main plane, and then the above purpose is accomplished.
