A Mo—Si—B-based alloy for a heat-resistant alloy that satisfies, more than conventional, physical properties such as proof stress and hardness adapted to an increase in the melting point of 5 a welding object. The Mo—Si—B-based alloy powder is such that the full width at half maximum of (600) of Mo5SiB2 in X-ray diffraction peak data is 0.08 degrees or more and 0.7 degrees or less.