Pipe connecting device

A pipe connecting device of the type using an inner ring is provided which, by reviewing once again the structure, has been improved so as to allow more repeated use than conventionally possible even while maintaining good seal performance. This pipe connecting device is provided with an inner ring (3) which has an outer peripheral part (3G) provided on the tip with a tapered outer peripheral expanded surface (3a) which expands a tube end (4C), a pipe fitting main body (1) which has a cylindrical screw portion (1A) with an attached male screw (7), and a union nut (2) which has a female screw (13). The inner ring (3) expands the tube end (4C) and is inserted into the cylindrical screw portion (1A), and the tapered outer peripheral expanded surface (3a) is pressed by the union nut (2) which is engaged and screwed onto the cylindrical screw portion (1A), the tapered outer peripheral expanded surface (3a) and the union nut (2) holding the tube (4) from both sides, wherein the tube pressing portion (12b) of the union nut (2) which presses the tube (4) between the tapered outer peripheral expanded surface (3a) is formed as an inclined inner peripheral surface which, relative to the axis (Y) of the cylindrical screw portion (1A), is inclined in the same direction as the outer peripheral expanded surface (3a).