An apparatus comprises two or more image processing units and a main merger unit. Each image processing unit comprises four information processing units and a sub merger unit for merging data output from the four information processing units. The main merger unit merges data output from multiple sub merger units. Data output from the information processing units are stored in parallel in a register on a unit length basis for serial transmission. Auxiliary data is added for identifying data that have been altered or modified. The serial data, with the auxiliary data added thereto, are output to the main merger unit.