A pattern generator includes a main memory for storing a plurality of sequence data blocks for generating a test pattern, a first sequence cache memory for sequentially storing the sequence data blocks, a second sequence cache memory, a data development section for sequentially executing the sequence data blocks stored in the first cache memory and generating a test pattern and a read-ahead means, when the data development section detects a read-ahead instruction on reading ahead the other sequence blocks during executing one sequence data block, for reading the other sequence blocks from the main memory and storing the same in the second sequence cache memory.