교화사 is not a common word. It is made up of the noun 교화 and the suffix 사.
교화 means educating someone to lead them in the right direction, a term often used in connection with delinquent juveniles or in a religious context. 교화하다 is the verb.
사 is a common suffix which can have two meanings in this context. It can mean either a member of a profession, as in 변호사(lawyer), 판사(judge), 조종사(pilot), 정비사(maintenance technician) and so on, or a certain history, as in 세계사(world history), 기독교사(Christian history), 변천사(history of changes), etc.
So 교화사 can be interpreted with either of these two meanings.
With the first meaning of 사, it would mean someone whose job is to educate and lead people for a religious or educational establishments. The other would be the history of educating and edifying people in such such institutions.