In one embodiment, a writing data generation method is for generating writing data used by a multi-charged particle beam writing apparatus. The writing data generation method includes referring to library data in which a vertex sequence including a plurality of vertices is registered, and extracting a portion of an outer line of a figure contained in design data, the portion corresponding to the vertex sequence, and representing the extracted portion by information which identifies the vertex sequence and information which indicates a connection method for the plurality of vertices of the vertex sequence, and generating the writing data.