A shaft seal apparatus comprising a mechanical seal device including: a stationary ring secured to a casing through a seal cover, said seal cover having a discharge hole and an inflow hole, and a rotary ring secured to a rotary shaft that rotates with respect to said casing, such that said rotary ring rotates together with said rotary shaft, and having a rotational sliding surface that slides on a stationary sliding surface of said stationary ring, characterized in that said seal cover covers over said rotary shaft so that a sealed space of sealed fluid sealed by sliding of said stationary sliding surface and said rotational sliding surface is formed over said rotary ring, wherein said sealed space is formed between an inner circumferential surface of said seal cover and said rotary shaft to communicate with the inside of said casing, and the fluid, which is the same as the processing fluid inside of the casing, is sealed by said mechanical seal device as sealed fluid, a pumping ring having a spiral projection on an outer circumferential surface is secured to said rotary shaft at an axial position different from said rotary ring, said spiral projection produces an axial flow of said sealed fluid positioned in said sealed space in accordance with said rotary shaft, on said inner circumferential surface of said seal cover, said inflow hole is formed at the upstream side of said spiral projection of said pumping ring, while said discharge hole is formed on said inner circumferential surface of said seal cover positioned in the downstream side of the axial flow of said sealed fluid resulting from a rotation of said pumping ring, said discharge hole being formed at the outer circumferential position of said rotary ring, and a baffle member having a flow guiding surface is mounted on the downstream position of said discharge hole, and said flow guiding surface is formed to protrude radially inward in order to block the flow of said sealed fluid along the rotating direction of said rotary shaft and guide the sealed fluid toward said discharge hole, wherein said sealed fluid in said sealed space being discharged from said discharge hole is returned to the inside of said sealed space via said inflow hole through an external piping. a stationary ring secured to a casing through a seal cover, said seal cover having a discharge hole and an inflow hole, and a rotary ring secured to a rotary shaft that rotates with respect to said casing, such that said rotary ring rotates together with said rotary shaft, and having a rotational sliding surface that slides on a stationary sliding surface of said stationary ring, said seal cover covers over said rotary shaft so that a sealed space of sealed fluid sealed by sliding of said stationary sliding surface and said rotational sliding surface is formed over said rotary ring, wherein said sealed space is formed between an inner circumferential surface of said seal cover and said rotary shaft to communicate with the inside of said casing, and the fluid, which is the same as the processing fluid inside of the casing, is sealed by said mechanical seal device as sealed fluid, a pumping ring having a spiral projection on an outer circumferential surface is secured to said rotary shaft at an axial position different from said rotary ring, said spiral projection produces an axial flow of said sealed fluid positioned in said sealed space in accordance with said rotary shaft, on said inner circumferential surface of said seal cover, said inflow hole is formed at the upstream side of said spiral projection of said pumping ring, while said discharge hole is formed on said inner circumferential surface of said seal cover positioned in the downstream side of the axial flow of said sealed fluid resulting from a rotation of said pumping ring, said discharge hole being formed at the outer circumferential position of said rotary ring, and a baffle member having a flow guiding surface is mounted on the downstream position of said discharge hole, and said flow guiding surface is formed to protrude radially inward in order to block the flow of said sealed fluid along the rotating direction of said rotary shaft and guide the sealed fluid toward said discharge hole, wherein said sealed fluid in said sealed space being discharged from said discharge hole is returned to the inside of said sealed space via said inflow hole through an external piping.