A flame hole unit structure of a combustion apparatus provided with a plurality of flame holes for forming a flame comprises: a lean flame hole unit including, as a flame hole for jetting lean gas, at least one lean flame hole extending along the longitudinal direction which is a direction perpendicular to the jetting direction of the lean gas; and a rich flame hole unit including, as a flame hole for jetting rich gas, a pair of rich flame hole provided on both sides of the lean flame hole unit with respect to a width direction which is a direction perpendicular to the jetting direction and the longitudinal direction and extending along a direction parallel to the longitudinal direction. When a region, which is defined at the top end of the rich flame hole by means of first and second lines that are arbitrary imaginary lines across the rich flame hole, and by means of a pair of rich flame hole walls spaced apart along the width direction and forming a part of the rich flame hole between the first and second lines, is referred to as a reference region, then the rich flame hole includes a region which is designed such that, at the time of generating the flame by the rich gas, between arbitrary reference regions of the same size, the sum of the amounts of heat transferred to the pair of rich flame hole walls forming each reference region is substantially the same.