add safe mode.
add safe mode.

murashitas/review,kmuto/review,kuad9/review_study,takahashim/review,krororo/review,kmuto/review,murashitas/review,masawada/review,krororo/review,orangain/review,kuad9/review_study,kmuto/review,masawada/review,suzuki/review,suzuki/review,takahashim/review,krororo/review,orangain/review