This invention is directed to a printing apparatus capable of simplifying the apparatus arrangement by using a common processing unit to execute different processes. To achieve this, a common processing unit is adopted to execute the first processing to perform multi-value/binary conversion of multi-valued data and the second processing to perform resolution conversion and thinning processing of binary data. In accordance with an instruction input from a user, it is controlled to execute either the first or second processing. An image is printed on a printing medium based on data obtained by executing the common processing unit.