It has been widely agreed that it is risky for patients with diabetes to drive during hypoglycemia. However, driving during non-hypoglycemia may also bring certain safety hazards for some patients with diabetes. Based on previous studies on diabetes-related to early aging effect, as well as gender differences in health belief and driving behavior, we have hypothesized that middle-aged male drivers with type 2 diabetes, compared with the control healthy ones, may experience a decline in driving performance without awareness. And the decline is caused by impaired perceptual and cognitive driving-related functions. To verify these hypotheses, we recruited 56 non-professional male drivers aged between 40 and 60 (27 patients with type 2 diabetes and 29 healthy controls) to perform a simulated car-following task and finish behavioral tests of proprioception, visual search, and working memory abilities during non-hypoglycemia. They also reported their hypoglycemia experience and perceived driving skills. We found that the patients had equal confidence in their driving skills but worse driving performance as shown in larger centerline deviation (t = 2.83, p = .006), longer brake reaction time (t = 3.77, p = .001) and shorter minimum time-to-collision (t = -3.27, p = .002). Such between-group differences in driving performance could be fully mediated by proprioception, visual search ability, and working memory capacity but not by hypoglycemia experience. Regarding the effect sizes of the mediation, the visual search ability played the most important role, and then followed the working memory and the proprioception. This initial study provides original and first-hand evidence demonstrating that the middle-aged male drivers with type 2 diabetes have deteriorated driving performance, but they are unaware of it. We will also discuss the possible measures to identify people of the highest risk and improve their safety awareness by using the findings of the current study.