A resistance adjusting type heater including a honeycomb structure having a large number of passages, at last two electrodes for energizing the honeycomb structure, and a resistance adjusting mechanism such as a slit provided between the electrodes to heat the gas flowing through the passages formed in the honeycomb structure. A catalytic converter includes a main monolith catalyst and the above-described heater placed adjacent to and upstream of the main monolith catalyst. A catalytic converter includes a honeycomb structure having a large number of passages, a catalyst carried on the honeycomb structure, at least two electrodes for energizing the honeycomb structure, and a resistance adjusting mechanism provided between the electrodes. A catalytic converter includes a main monolith catalyst, and a heater placed adjacent to and upstream of the main monolith catalyst. The heater includes a honeycomb structure having a large number of passages, a catalyst carried on the honeycomb structure, at least two electrodes for energizing the honeycomb structure, and a resistance adjusting mechanism provided between the electrodes.