A catalyst apparatus is disposed in an exhaust passage for exhaust gas discharged from an internal combustion engine and includes a catalyst section for purifying the exhaust gas, and a heater section disposed upstream of the catalyst section in the exhaust passage and adapted to heat the exhaust gas. The heater section is configured such that a plurality of metal thin plates and insulators are stacked alternatingly are wound. The heater section contains a pair comprising a positive electrode and a negative electrode for energizing and heating the metal thin plates. The positive and negative electrodes are joined to each of the metal thin plates in such a manner that the positive electrode is located away from the negative electrode in a winding direction of the metal thin plates.