Approximate computing is an efficient approach for error-tolerant applications because it can trade off accuracy for power. Addition is a key fundamental function for these applications. In this paper, we proposed a low-power yet high-speed accuracy-configurable adder that also maintains a small design area. The proposed adder is based on the conventional carry look-ahead adder, and its configurability of accuracy is realized by masking the carry propagation at runtime. Compared with the conventional carry look-ahead adder, with only 14.5% area overhead, the proposed 16-bit adder reduced power consumption by 42.7%, and critical path delay by 56.9% most according to the accuracy configuration settings, respectively. Furthermore, compared with other previously studied adders, the experimental results demonstrate that the proposed adder achieved the original purpose of optimizing both power and speed simultaneously without reducing the accuracy.