The invention provides catalysts which are not corroded in acidic electrolytes or at high potential and have excellent durability and high oxygen reducing ability. The catalysts include a niobium-containing oxycarbonitride having I2/(I1+I2) of not less than 0.25 wherein I1 is the maximum X-ray diffraction intensity at diffraction angles 2θ of 25.45 to 25.65 degrees and I2 is the maximum X-ray diffraction intensity at diffraction angles 2θ=2θ of 25.65 to 26.0 degrees according to X-ray powder diffractometry (Cu—Kα radiation).