Disclosed is, as a high-strength steel plate of API X80 grade or higher with a thickness of 38 mm or more, a thick steel plate for structural pipes or tubes that exhibits high strength in the rolling direction, excellent Charpy properties at its mid-thickness part, and high material homogeneity without addition of large amounts of alloying elements. The thick steel plate for structural pipes or tubes disclosed herein has: a specific chemical composition; a microstructure mainly composed of bainite; a tensile strength of 620 MPa or more; a Charpy absorption energy vE−20° C. at −20° C. at the mid-thickness part of 100 J or more; a variation of Vickers hardness in a plate thickness direction ΔHV10,t of 50 or less; and a variation of Vickers hardness in a plate widthwise direction ΔHV10,c of 50 or less.
