A niobium primary powder having an average particle size of 0.01 to 0.5
.mu.m and an average circular degree of 0.8 or more, the circular degree
being defined by 4 .pi.A/L.sup.2 (wherein A is an area of a solid
projected on a plain face and L is an outer circumferential length of the
projection view); a niobium primary agglomerated powder having an average
particle size of 0.03 to 20 .mu.m, which is an agglomerate of the niobium
primary powder; a niobium secondary agglomerated powder having an average
particle size of 50 to 150 .mu.m, which is obtained by granulating the
primary agglomerated powder; a sintered body of the niobium primary
agglomerated powder or niobium secondary agglomerated powder; and a
capacitor using the sintered body. By using sintered bodies of the niobium
primary agglomerated powder or niobium secondary agglomerated powder, a
capacitor having a large capacitance per unit volume and good voltage
resistance can be manufactured.
