Provided is a water absorbent sheet retaining mat which can retain a water absorbent sheet easily and surely. A water absorbent sheet retaining mat M1, M2, M3, M4 for retaining a water absorbent sheet Sa1 having a first polygonal contour, comprises: a mat member Pm1, Pm2, Pm3, Pm4 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 Pr1, Pr2, Pr4 having a slit member S comprised of at least one slit formed in a top surface Sru at a first predetermined height t2 from the second main plane Sb for accepting a part of perimeter of the water absorbent sheet Sa1 being inserted therein.
