A medical instrument system includes an elongated member having an inner space in a direction of a longitudinal axis, an insertion section installed at the inner space and having a bending section capable of being bent, a manipulation section configured to manipulate the bending section, a first manipulation member transmitting a driving force of the bending section in accordance with the manipulation by the manipulation section, a second manipulation member arranged in the direction of a longitudinal axis, a connecting section having a first connecting section and a second connecting section and capable of connecting the first manipulation member and the second manipulation member, and a switching mechanism having a first acting section and a second acting section and switching between a connection state and a release state in accordance with a relative movement between the elongated member and the insertion section.