A communication device according to the present invention includes: a receiving unit which receives a block transmitted by a communication device; a photocurrent measuring unit which measures a reception quality of the received block; a PHY rate determining unit which determines, based on the reception quality, a PHY rate that is used by the communication device for transmitting a next block; a block size control unit which determines, based on the measured reception quality, a block size; and a transmission unit which transmits feedback information including the determined PHY rate and the determined block size to the communication device, and the block size control unit determines the block size to be a value smaller than a maximum value of a block size that can be transmitted by the communication device, when a value indicating the reception quality of the block is within a predetermined range including a PHY rate threshold.