Provided are an apparatus and a method for effectively managing threads diverged by a conditional branch based on Single Instruction Multiple-based Data (SIMD). The apparatus includes: a plurality of Front End Units (FEUs) configured to fetch, for execution by SIMD lanes, instructions of thread groups of a program flow; and a controller configured to schedule a thread group based on SIMD lane availability information, activate an FEU of the plurality of FEUs, and control the activated FEU to fetch an instruction for processing the scheduled thread group.