According the present invention, an alloy powder for overlay welding that prevents generation of gas defects in a weld overlay alloy in order to improve the toughness and wear resistance of the weld overlay alloy is provided. The alloy powder is an alloy powder for overlay welding on a steel surface containing nitrogen, which is characterized in that it contains 30% to 45% by mass of Mo, 10% to 30% by mass of Ni, 0.2% to 0.6% by mass of C, and 0.30% to 2.0% by mass of Al, with the balance made up of incidental impurities and Co.