A hydrogel according to the present invention has a polymer matrix obtained by polymerizing an acrylic monomer, an acrylic monomer, water, and a polyhydric alcohol, and the content of the acrylic monomer is 100 to 2000 ppm.本發明之水凝膠係具有使丙烯酸系單體聚合而成之高分子基質、丙烯酸系單體、水、及多元醇,其中,丙烯酸系單體之含量為100至2000ppm。