With the accumulation of clinical trials demonstrating its efficacy and safety, peroral endoscopic myotomy (POEM) has emerged as a less invasive treatment option for esophageal achalasia compared with laparoscopic Heller myotomy. However, the difficulty in determining the exact extent of myotomy, a critical factor associated with the success and safety of the procedure, remains a limitation. Although the various endoscopic landmarks and ancillary techniques have been applied, none of these has been proven sufficient. As a solution for this limitation, the double-scope POEM technique with a second endoscope to assure the exact length of the submucosal tunnel has been applied since 2014. Before double-scope POEM was introduced, the second endoscope was applied only to confirm the accuracy of the procedure. In the present study, we performed double-scope POEM in the treatment of esophageal achalasia through a novel procedure of simultaneous application of the second endoscope to assist in the conventional POEM procedure.