A rotary machining device comprising: a reference axis; and a support jig which supports a workpiece such that a central axis of the workpiece and the reference axis are coaxial with each other; a shaft-equipped spherical seat which includes a machining portion having a central axis inclined with respect to the reference axis and formed at one axial end portion, and a convex spherical portion having a partially spherical shape, formed at an axially intermediate portion and facing upwards; a concave spherical seat including an insertion hole through which an axially intermediate portion of the shaft-equipped spherical seat is inserted, and a concave spherical portion which spherically engages with the convex spherical portion ; an oil receiver having an annular recess portion which faces an entire circumference of an outer circumferential edge of the concave spherical portion ; a guide member which guides lubricating oil, which has flowed out from a spherical engagement portion between the convex spherical portion and the concave spherical portion , toward the annular recess portion , a base end portion of the guide member being supported by a lower side portion of the convex spherical portion ; and an annular cover plate , supported and fixed on an inside of the oil receiver in a radial direction, wherein the cover plate has an annular cover portion and a return portion , the cover portion being slightly inclined in the downward direction as it goes radially outward such that the lubricating oil, which falls on the cover portion , flows into the oil receiver , and the return portion being bent upward from a radially inner end portion of the cover portion . a reference axis; and a support jig which supports a workpiece such that a central axis of the workpiece and the reference axis are coaxial with each other; a shaft-equipped spherical seat which includes a machining portion having a central axis inclined with respect to the reference axis and formed at one axial end portion, and a convex spherical portion having a partially spherical shape, formed at an axially intermediate portion and facing upwards; a concave spherical seat including an insertion hole through which an axially intermediate portion of the shaft-equipped spherical seat is inserted, and a concave spherical portion which spherically engages with the convex spherical portion ; an oil receiver having an annular recess portion which faces an entire circumference of an outer circumferential edge of the concave spherical portion ; a guide member which guides lubricating oil, which has flowed out from a spherical engagement portion between the convex spherical portion and the concave spherical portion , toward the annular recess portion , a base end portion of the guide member being supported by a lower side portion of the convex spherical portion ; and an annular cover plate , supported and fixed on an inside of the oil receiver in a radial direction, wherein the cover plate has an annular cover portion and a return portion , the cover portion being slightly inclined in the downward direction as it goes radially outward such that the lubricating oil, which falls on the cover portion , flows into the oil receiver , and the return portion being bent upward from a radially inner end portion of the cover portion . <EOS>