Patients with type 2 diabetes who require insulin therapy are commonly elderly and have poor visual acuity. In this study, we examined the clinical usefulness of the indicator magnifying window (IMW) for elderly patients with type 2 diabetes. We recruited 50 patients with type 2 diabetes over the age of 60 who had used insulin pens for glucose control. They were asked to set the insulin pen at randomly selected doses with or without an IMW. We assessed dosing accuracy, convenience, self-confidence, need for eyeglasses, preference, and willingness to recommend the IMW to other patients. Although the IMW did not improve the dosing accuracy or convenience, it significantly decreased the need for eyeglasses. Overall, the clinical usefulness of the IMW is quite limited in elderly patients with type 2 diabetes.