Diabetic muscle infarction (DMI) is a rare condition that usually occurs in diabetic patients who have longstanding microvascular complication. The typical presentation is a painful swelling with abrupt onset in the lower limbs, particularly involving hyper-intense signals in T2-weighted magnetic resonance imaging (MRI) images. The treatment consists of bed rest, analgesics, and physical therapy. The authors encountered a case of DMI with bilateral tender swelling on the anteromedial aspect of the thighs. DMI is less likely to develop in patients with good glycemic control. Recently, however, a few cases demonstrated that DMI can also develop in patients with good glucose control. However, diffuse and extensive infarction of muscle, such as in our case, is rare. It is important to consider differential diagnoses in order to avoid misdiagnosis and non-essential treatment such as overuse of antibiotics or steroid treatment. In this case, we diagnosed the patient using MRI, muscle biopsy, and electromyography and successful treatment involved bed rest and analgesics. We herein report a case of 76-year-old man with very extensive and diffuse DMI in spite of well-controlled type 2 diabetes.