A bit block transfer (Bitblt) circuit includes a read register, a write register, a bit shifting circuit and an overflowing register. The read register stores decomposition data including original data. The bit shifting circuit shifts the decomposition data in the read register to the write register and shifts bits of the decomposition data in the write register such that an initial bit of the original data of the decomposition data is situated apart from an initial address of the write register by a bit-shifting amount. The overflowing register coupled to the write register stores overflowing data of the original data overflowing from a memory length of the write register when the bits of the decomposition data in the write register are being shifted. The write register outputs and writes the decomposition data therein to a memory cell of a first memory.