It is known that designers employ a wide range of visual representations in order to tackle ill-determined problems that are known as the wicked problems. In addition, a sketch is typically employed among such visual presentations in the early stage of a design. Therefore, systematic analysis of the sketches that designers produce in their practice could be a means of understanding how designers think during the conceptual phase of a design. Hence, this paper explores designer sketches from two perspectives. First, preceding research concerning analyses of designer sketches that were carried out in the fields of architectural design and engineering design was extensively reviewed and analyzed. Secondly, on the basis of studies of industrial designers activities in his/her practice, methods for sketch analysis and its application are proposed. This study also structures a conceptual framework for the analysis of the sketches of industrial designers. This framework and method of this analysis will make a contribution toward a profound understanding of the characteristics of industrial designer's ways of thinking as well as toward pedagogical applications of this work.