A mechanism for generation of two concentric pulsar beams corresponding to the core and conal pulsar emission is proposed. The inner beam originates close to the star, where the radius of curvature of the dipolar magnetic field lines is suitable for coherent curvature emission at pulsar radio frequencies. Further from the star where the outer beam originates, the radius of curvature of dipolar lines is probably too large, but the actual curvature can be dominated by the toroidal component of field lines twisted back due to the pulsar rotation. One can show that for even moderate twisting the actual radius of curvature leads again to pulsar radio frequencies. Thus, the pulsar emission is a superposition of two beams originating at widely radially separated locations. When the observer's line-of-sight cuts both beams, a three-component profile should be observed. Because of the retardational time delay, the inner (core) component should appear late with respect to the profile midpoint, that is, closer to the traling component. Such an asymmetry is indeed observed in complex profile pulsars. In pulsar magnetosphere, the radius of curvature of dipolar field lines depends on the radius of the emission region in the opposite way than that of the toroidal lines. This explains why core and conal components dominate the mean profile at low and high frequencies, respectively.