A beam-column joint structure (1) including: a column (11) and an I-beam (212) with a pair of beam flanges (216) of the I-beam joined directly to joint plates (16) of the column main body via a welded section (218); wherein at the intersect position (P1), the ratio of the full plastic strength of the column relative to the full plastic strength of the beam is 1.5 or more and 3.0 or less, and the ratio of the full plastic strength of the beam relative to the full plastic strength of a portion (17a) of the column in the range of the height of the beam in the vertical direction is 1.05 or more and 1.5 or less.