To provide an adhesive capable of forming an adhesive layer which can be stuck to an adherend without including any bubbles and can be peeled off without leaving any residual adhesive, and to provide a surface protection sheet comprising the adhesive, in particular, a surface protection adhesive sheet suitable for protecting a photomask surface.

The adhesive comprises an acrylate resin with a weight-average molecular weight, which is measured as polystyrene-equivalent molecular weight based on the GPC method, of 500,000-1,000,000, a cross-linking agent and a photopolymerization initiator. When the adhesive is immersed in ethyl acetate at 23C for 24 hr and subsequently removed from ethyl acetate and dried at 110C for 1 hr, it achieves a specific gel fraction rate, represented by a specific expression, depending on whether it is exposed or not exposed to UV irradiation.