To prevent a medical apparatus such as an endoscope or an electrophysiological catheter that includes an insertion portion to be inserted into the body of a patient from breaking at any unexpected positions. A medical apparatus includes a bendably deformable portion, a deforming-force-transmitting mechanism that is connected to a part of the bendably deformable portion, and an operation portion that applies a deforming force or a shape retaining force to the bendably deformable portion by controlling a tension applied to the deforming-force-transmitting mechanism. The deforming-force-transmitting mechanism includes a tension reducing mechanism.