A niobium powder comprising at least one element selected from the group consisting of chromium, molybdenum, tungsten, boron, aluminum, gallium, indium, thallium, cerium, neodymium, titanium, rhenium, ruthenium, rhodium, palladium, silver, zinc, silicon, germanium, tin, phosphorus, arsenic, bismuth, rubidium, cesium, magnesium, strontium, barium, scandium, yttrium, lanthanum, praseodymium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium, lutetium, hafnium, vanadium, osmium, iridium, platinum, gold, cadmium, mercury, lead, selenium and tellurium; a sintered body of the niobium powder; and a capacitor comprising a sintered body as one electrode, a dielectric material formed on the surface of the sintered body, and counter electrode provided on the dielectric material.