Provided is a planar paper for an adhesive tape, and an adhesive tape utilizing such planar paper as a backing, which has an elongation sufficient to allow the adhesive tape to be favorably adhered to an adherend surface without being accompanied by any lift and separation, but with consistently conforming to the curved surfaces and/or the rough surfaces; which is capable of providing a clear painting line left in a portion of a painted layer required in automobiles; which is capable of being easily cut by hand without requiring any tool as a blade; and which is also excellent in handleability. The planar paper comprises a polyvinyl alcohol-series fiber having a fiber breaking temperature in water of 92 to 125° C., a tenacity of 0.5 to 3.5 cN/dtex at 10% elongation, and a breaking elongation of 17 to 60%.