A superconducting magnet device with which device breakage caused by a quench can be avoided while helium consumption is reduced. A sheet-like convection-preventing member is disposed at least either above or below a heat transfer member transferring to gaseous helium heat transferred from the outside, so as to cover a helium gas release tube for the gaseous helium, and thus heat exchange performance during transportation is improved. In the case where the quench occurs, the convection-preventing member is lifted upward in the release tube, thereby ensuring to provide a flow path for the gaseous helium and avoiding excessive increase of the internal pressure.