To provide through hole reinforcing structure making it easy to machine reinforcing bars.

Through hole reinforcing structure is provided with four reinforcing bars 10A, 10B, 20A, 20B. These reinforcing bars 10A, 10B, 20A, 20B have half ring parts 11, 21 of semicircular shape and a pair of extension parts 12, 22 extended in the tangential direction from both end parts of the half ring parts 11, 21. The reinforcing bars 10A, 20A are so arranged that the half ring parts 11, 21 circulate a semicircle around the left side of a through hole H. The reinforcing bars 10B, 20B are so directed that the half ring parts 11, 21 circulate a semicircle around the right side of the through hole H and abut the back side of the reinforcing bars 10A, 20A. A small diameter ring 13 is formed of the half ring parts 11 of the reinforcing bars 10A, 10B, and a large diameter ring 23 is formed of the half ring parts 21 of the reinforcing bars 20A, 20B.