To provide a communication device capable of bidirectional communication using ultrasonic waves by a simple configuration.
A master unit 10 which communicates with a slave unit 60 by ultrasonic waves underwater includes: a communication unit 20 for transmitting and receiving information using ultrasonic waves; a memory 40 for storing a table to which slots having a first time length and instructing communication with the slave unit 60 are time-sequentially allocated and which is in common with the slave unit 60; a control unit 35 for synchronizing with the slave unit 60 and instructing the transmission and reception of the information to the communication unit 20 corresponding to the first time length on the basis of the slots arranged in the stored table; and a slot length decision unit 55 for determining a second time length on the basis of the time required for the transmission and reception with the slave unit 60. The control unit 35 instructs the transmission to the slave unit 60 of the information regarding the second time length and instructs the transmission and reception of the information based on the slots corresponding to the second time length.
Osamu Suzawa
Kazuhiko Miyasaka