An inspection system includes a display device including a nonvolatile memory, an inspection device configured to generate a writing voltage for application to the nonvolatile memory, and a protection part configured to apply the writing voltage to the nonvolatile memory when the writing voltage is within an allowable voltage range, and not to apply the writing voltage to the nonvolatile memory when the writing voltage is not within the allowable voltage range. The application of the writing voltage to the nonvolatile memory enables a multi-time programming (MTP) operation in which reference data writes to the nonvolatile memory.