To provide a rotary joint device, in which upon reassembling each of cylindrical blocks of an outer cylinder after the blocks have been once disassembled, an assembled state after the blocks are reassembled can be made coincident with an assembled state before the blocks are disassembled with high accuracy.

A rotary joint device includes: a plurality of attachment grooves 81 formed at a plurality of positions on an outer circumferential surface of an outer cylinder 61, the attachment grooves being formed so as to straddle two adjoining cylindrical blocks 61a, 61b, 61c to be exposed on the outer circumferential surface of the outer cylinder, and each attachment groove having a bottom surface 82 that is machined to form a flat surface in a state in which the two cylindrical blocks are combined; and a plurality of positioning blocks 80 corresponding to the plurality of attachment grooves on a one-to-one basis and having an attachment phase that is uniquely set with respect to the attachment grooves in an axial direction and in a circumferential direction of the outer cylinder, each positioning block having an attachment surface machined into a flat surface, corresponding to the bottom surface of the corresponding attachment groove.