An object is to provide a hydrogel, which is excellent in adhesiveness to an electrode element, less reduced in tackiness and adhesiveness to an electrode element and an object even if it absorbs water such as sweat and moisture, as well as has an optimal adhesive force to the skin surface and gives no damage to the skin when removed. A hydrogel 1 having a laminate structure of layer A 10 and layer B 20, wherein layer A 10 contains a monomer-derived component, water, a humectant, a water-insoluble polymer having tackiness and an amphiphilic polymer, the water-insoluble polymer is contained in a proportion of 3 to 20 wt% based on a total amount of layer A, and the amphiphilic polymer is a polyvinyl alcohol having a saponification degree of 50 to 75% and is contained in a proportion of 0.05 to 5 wt% based on the total amount of layer A； layer B 20 contains a monomer-derived component, water and a humectant and is substantially free of a water-insoluble polymer having tackiness and a polyvinyl alcohol； an amount of the water based on a total amount of layer B is the amount of water based on the total amount of layer A ± 10 wt%； and an amount of the humectant based on the total amount of layer B is an amount of the humectant based on the total amount of layer A ± 10 wt%.
