A flash memory device is disclosed. The memory cell array has a first plane and a second plane and stores a first data unit and a second data unit. The data register buffers the first data unit and the second data unit transmitted from the memory cell array when a read command or a data toggle command is received and stored by the command register. The control circuit performs a data toggle operation to control the data register selecting and transferring the first data unit and the second data unit to the I/O control circuit to make the I/O control circuit sequentially transmit the first data unit and the second data unit to the flash memory controller through a specific communication interface in response to the read command or the data toggle command. The transmission of the first data unit is followed by the transmission of the second data unit.