A mechanism is proposed that reduces power consumption, and which focuses on the Speculative Execution Depth (SED). SED is the number of branch instructions whose results are not yet known in the processor. The mechanism controls the SED depending on the current workload. The evaluation results show that the proposed scheme can reduce power consumption by 10.8–41.0% when the target throughput ranges from 60–90%, and suppress the average error margin with the target throughput to 1.0% or less.