A storage device includes a nonvolatile memory device, and a controller that reads first data from the nonvolatile memory device. When a number of first errors of the first data is not smaller than a first threshold value, the controller determines whether the first errors include timing errors arising from a variation of signal transmission timings between the nonvolatile memory device and the controller and performs a retraining operation on the signal transmission timings when the first errors include the timing errors.