A communication apparatus comprising: a communication unit being adapted to transmit and to receive a radio wave; a controller; and a measuring unit, characterized in that the controller is adapted to perform the following: determine, according to a first reference of received signal strength in one communication apparatus which is either an external communication apparatus or the communication apparatus when in a predetermined communication state with the external communication apparatus through the communication unit, a transmitted signal strength for a transmission radio wave from the other communication apparatus which is either the communication apparatus or the external communication apparatus as a first reference of transmitted signal strength; determine a second reference of transmitted signal strength between the first reference transmitted signal strength and a maximum strength of transmitted signal strength from the other communication apparatus; and determine the received signal strength for the transmission radio wave in the second reference of transmitted signal strength in the predetermined communication state as a second reference of received signal strength; and when a predetermined condition is satisfied, obtain a received signal strength of the one communication apparatus for the transmission radio wave in the second reference of transmitted signal strength and determine a transmitted signal strength of a transmission radio wave from the other communication apparatus according to a comparison between the received signal strength and the second reference of received signal strength, wherein the controller is adapted to determine that the predetermined condition is satisfied when it is determined that a communication situation has changed according to data measured by the measuring unit, said data indicating a non-continuous change of the state of the communication apparatus detected by sensors (231, 232, 233) comprised in the measuring unit, said sensors (231, 232, 233) being adapted to measure various physical quantities. a communication unit being adapted to transmit and to receive a radio wave; a controller; and a measuring unit, characterized in that the controller is adapted to perform the following: determine, according to a first reference of received signal strength in one communication apparatus which is either an external communication apparatus or the communication apparatus when in a predetermined communication state with the external communication apparatus through the communication unit, a transmitted signal strength for a transmission radio wave from the other communication apparatus which is either the communication apparatus or the external communication apparatus as a first reference of transmitted signal strength; determine a second reference of transmitted signal strength between the first reference transmitted signal strength and a maximum strength of transmitted signal strength from the other communication apparatus; and determine the received signal strength for the transmission radio wave in the second reference of transmitted signal strength in the predetermined communication state as a second reference of received signal strength; and determine, according to a first reference of received signal strength in one communication apparatus which is either an external communication apparatus or the communication apparatus when in a predetermined communication state with the external communication apparatus through the communication unit, a transmitted signal strength for a transmission radio wave from the other communication apparatus which is either the communication apparatus or the external communication apparatus as a first reference of transmitted signal strength; determine a second reference of transmitted signal strength between the first reference transmitted signal strength and a maximum strength of transmitted signal strength from the other communication apparatus; and determine the received signal strength for the transmission radio wave in the second reference of transmitted signal strength in the predetermined communication state as a second reference of received signal strength; and when a predetermined condition is satisfied, obtain a received signal strength of the one communication apparatus for the transmission radio wave in the second reference of transmitted signal strength and determine a transmitted signal strength of a transmission radio wave from the other communication apparatus according to a comparison between the received signal strength and the second reference of received signal strength, wherein the controller is adapted to determine that the predetermined condition is satisfied when it is determined that a communication situation has changed according to data measured by the measuring unit, said data indicating a non-continuous change of the state of the communication apparatus detected by sensors (231, 232, 233) comprised in the measuring unit, said sensors (231, 232, 233) being adapted to measure various physical quantities.