A device (1) has a first mechanical seal (2) provided with a second mechanical seal. A guide surface (30D) is provided on the outer periphery of a support surface (30H), where the outer surface surrounds a shaft (70) and extends toward the outside (O) of a machine. The support surface is located on the side opposite to an installation surface (30A) installed on an outer surface (60A) of a device body (60). The first mechanical seal (2) includes a relative seal surface (10A) having a support section (30P) where the guide surface (30D) is provided and also includes a pair of seal surfaces (3A). The second mechanical seal has an annular shutoff seal section (15) having on its rear surface a pressing surface (15H) facing the support surface (30H), having on its front end surface a facing seal surface (50B) and a pair of shutoff seal surface (15A), and having a seal inner peripheral surface (15C) movably fitting to the guide surface (30D) in a sealed manner. The surface pressure of the shutoff seal surface (15A) of the second mechanical seal pressed, after being adjusted by spring means and/or fluid pressure, by the pressing surface (15H) of the shutoff seal section (15) is reduced to a level smaller than the surface pressure of the seal surfaces (3A) of the first mechanical seal (2). As a result, durability is improved, and even if sealed fluid leaks from the first mechanical seal (2), the leakage is sealed by the second .