To provide a synthetic resin extruded molding superior in water resistance, and suitable for various uses such as a building material such as a floor material, a wall material, a ceiling material and windows and doors, a vehicular interior trim material, and a part and a casing of an electric machine apparatus, without causing thrusting-up by the thermal expansion.

On one side surface provided with a downward recessed part, a cushion material is extendedly arranged toward the end side from the inside of the recessed part in a range without exceeding in both a width and the depth of the recessed part. The width of the recessed part is characterized by being formed narrower than the total of a width of a projection part and the thickness of the cushion material, and wider than the total of the width of the projection part and the thickness when thinned by pressing the cushion material.