A flow control of molten steel in a continuous slab caster mold has been carried out with travelling magnetic field. The aim of flow control is prevention against mold powder entrapment into molten steel. The travelling magnetic field was imposed to spouting stream from a submerged entry nozzle with the linear-motor-type actuator. This actuator has two travelling modes of magnetic field. One is for braking the velocity of spouting stream (EMLS: Electromagnetic Level Stabilizer), and another is for acceleration (EMLA: Electromagnetic Level Accelerator). With these braking and accelerating performance, control of steel flow velocity just below meniscus was carried out. By velocity measurement below molten steel surface at a commercial caster mold, performance of EMLS and EMLA was investigated. Especially for EMLS performance, change in meniscus velocity profile along mold width direction was examined. When increasing the intensity of EMLS, at first the meniscus velocity around a submerged entry nozzle was reduced and then the meniscus velocity around the mid of half width of a mold, hereafter the velocity around narrow face of a mold was reduced. Moreover formularization of the braking performance of meniscus velocity by EMLS was carried out. In this formula the braking performance was divided into two factors. By using the EMLS and EMLA with a computer control system, the surface defect frequency on cold rolled coil was reduced drastically.