A Co based alloy powder includes between 0.08% and 0.25% mass of carbon, 0.1% mass or less of boron, between 10% and 30% mass of chromium, 5% mass or less of iron, and 30% mass or less of nickel; the iron and the nickel in a total amount of 30% mass or less; includes at least one of tungsten and molybdenum in a total amount of between 5% and 12% mass; includes at least one of titanium, zirconium, niobium, tantalum, hafnium, and vanadium in a total amount of between 0.5% mass and 2% mass; includes 0.5% mass or less of silicon, 0.5% mass or less of manganese, and between 0.003% and 0.04% mass of nitrogen; and includes cobalt and impurities as the balance of the powder. Crystal grains included in the cobalt-based alloy powder have segregated cells; the cells have an average size of between 0.15 μm and 4 μm.