To provide a transfer mask data creating device and a method thereof which are capable of shortening the time required for creating mask data for manufacturing the EB transfer mask of an LSI (large-scale integrated circuit) chip with a prescribed H block mounted thereon.

The transfer mask data creating device 1 is equipped with a whole chip data creating portion 10 creating the whole chip mask data on the basis of design information on a chip; an H block data creating portion 30 which creates transfer basic data on a functional block, stores the data in a first memory portion 40, and registers the data as the H block in a second memory portion 50; and a data storage portion 70 which stores data on the whole chip masks. The whole chip data creating portion 10 is equipped with a first data acquisition portion 11 acquiring design information, a retrieving/processing portion 12 which checks whether a chip includes the H block or not, a data separating portion 13, a first region processing portion 14, a second region processing portion 15, and a mask processing portion 16.