To prepare a surface protective film which has initial adhesion necessary at the time of cutting processing and in other processing steps and is easily releasable from an adherend synthetic resin plate even after heating processing and, in addition, does not stain the adhered surface.

In the surface protective film obtained by laminating a pressure- sensitive adhesive layer on one side of a substrate material layer composed of a thermoplastic resin, the pressure-sensitive adhesive layer is obtained by admixing (a) 75-95 wt.% polyethylene based resin having one crystalline melting peak in the differential scanning calorimetry, a temperature width from the crystalline melting peak temperature to the temperature of completion of molding all crystals of at most 20°C, and a density of 0.900-0.920 g/cm3, (b) 5-25 wt.% polyethylene based resin having one crystalline melting peak in the differential scanning calorimetry, a temperature width from the crystalline melting peak temperature to the temperature of completion of melting all crystals of at most 20°C, and a density of less than 0.900 g/cm3, and (c) 0.1-4.0 pts.wt., based on 100 pts.wt. total amount of polyethylene based resins (a) and (b), tackifying resin.