A method of continuous casting of a steel employs a mold power having a viscosity of 0.5-1.5 poise at 1,300°C and a solidification temperature of 1,190-1,270°C, in which the mass ratio of CaO to SiO 2 is 1.2-1.9, and casting is carried out under the following conditions: casting speed is 2.5-10 m/minute; mold oscillation stroke is 4-15 mm; and specific cooling intensity in secondary cooling of a slab is 1.0-5.0 liter/kg-steel.