To automatically remove a foreign matter held between relay contacts associated with motor feeding of a motor driven power steering device while suppressing the further degradation of the relay contacts as much as possible.

The cumulative frequency of repetitive diagnosis is rewritably stored in a storage part 49; the cumulative frequency is set to an actual frequency smaller than the upper limit frequency until the cumulative frequency reaches the upper limit frequency every time a CPU 41 executes a diagnosis processing; the allowable frequency of the repetitive diagnosis is decided wherein the cumulative frequency, upon reaching the limit frequency, is set to zero at every diagnosis processing; the repetitive frequency of the diagnosis at every diagnosis processing is calculated as a retry frequency; the diagnosis processing is prohibited and finished; when the retry frequency reaches the allowable frequency; and the cumulative frequency stored in a storage part 48 is rewritten to the cumulative frequency updated by adding the retry frequency upon finishing the diagnosis processing, whenever the diagnosis processing is finished, preventing the on/off switching of the relay contact after the cumulative frequency reaches the upper limit frequency.

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