Test pieces of different thickness were heated by electric current with various power functions. Pool and flow boilings of water were studied at atmospheric pressure. In subcooled boiling, heat transfer rate is fairly high even after the DNB (Departure from Nucleate Boiling) point. DNB heat flux increases up to a saturation value with increasing test piece thickness. When power has maintained a non-zero level before the transient starts, the DNB heat flux is considerably reduced. A model analysis of transient saturated pool boiling is developed. The calculated results are compared with experimental data.