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 (21, 21a, 21b) 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 (21, 21a, 21b) 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 (21, 21a, 21b) 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 (21, 21a, 21b) 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.