The usefulness of cases in creative generation has been widely discussed and well recognized. However, it has been also experimentally indicated that introducing cases can limit human creative generation. In this study, we investigate the effects of case presentation in the task domain of generating mathematical word problems. Mathematical word problems have two essential attributes: surface problem situations and the mathematical structures of solutions, the control of which is recognized as an important issue in learning mathematics. In response, we present problems as cases to participants while controlling those attributes, with the results indicating that such presentation actually provides different constraining effects based on the control to their problem generation. Based on the results, we propose a support system for generating word problems, which presents problems as cases by controlling similarities.