A protein complex that binds to the Swi4/6 cell cycle box (SCB) promoter element, consensus sequence CRCGAAA, and activates transcription during the G1/S transition of the cell cycle. In Saccharomyces, the complex contains a heterodimer of the DNA binding protein Swi6p and the activator Swi4p, and is associated with additional proteins known as Whi5p and Msa1p.