A simple road traffic sign board fastening device comprises a fixing frame (9) and a sign board support (8), wherein a vertical column (92) of the fixing frame (9) is internally provided with a clamping groove (920) formed by an upper clamping part (921), a middle slope transition part (922) and a lower wide opening part (923) which are sequentially arranged from top to bottom; a clamping head (91) is arranged at the end part of the left side of a horizontal cross rod (82) of the sign board support (8) and is used for penetrating through the vertical column (92) from the lower wide opening part (923), the clamping head can move in the clamping groove (920) upwards to the inside of the upper clamping part (921), so that the clamping head (91) is stopped in the axial direction of the horizontal cross rod (82), and location in a front-back direction orthorhombic to the axial direction of the horizontal cross rod (82) can be achieved.