section manager in charge
A section manager who is responsible for a specific task, project, or area. Often used in business contexts to designate the person overseeing a particular matter.
For this matter, please contact the section manager in charge, Mr. Tanaka.
課長 is a general section manager, while 担当課長 specifies a section manager who is in charge of a particular task or area.
担当者 is a person in charge (not necessarily a manager), while 担当課長 is specifically a section manager with that responsibility.
Compound of 担当 (たんとう, 'in charge') and 課長 (かちょう, 'section manager').