managing director

pls read section 165, which says that a person can act as director for not more than 10 public and 10 private companies.
further, section 203 provides for appointment of KMP(MD in your case). now, section 203(3) says MD shall not hold offc in more than One Co.(he can act as MD for its Subsidiaries).

further, the 3rd proviso says that, if Entire Board who are present at meeting can Authorize/approves a person (who is already MD of other Co.) to act as MD.

Hence, a person who is Already an MD of one Co. can become MD of other companies, provided ALL the director's present at meeting agrees for it.
hope I have answered your question.

regards