A wireless terminal device for an interfering system that shares at least a part of a frequency band with an interfered system, comprising: a sensing period information setting part for setting sensing period information that indicates a sensing period for sensing a signal which is sent from a device of the interfered system and received by the wireless terminal device using the shared frequency band; an RF part configured to perform reception processing of a wireless signal via an antenna; a PHY processing part configured to perform reception processing in a physical layer; a MAC processing part configured to perform reception processing in a MAC layer and control the reception timing of reception data; a transmission power controlling part for controlling a transmission power; a sharing condition calculating part for using the sensing result by a sensing part as a basis to determine a sharing condition; and further comprising: the sharing condition containing at least transmission power information as a condition for transmission with use of the shared frequency band; the sensing period information setting part is configured to stop the function of the transmission power controlling part until an end of the sensing period to prohibit transmission; the wireless terminal device further comprising: the sensing part configured to sense the signal from the device of the interfered system in a state where the transmission is stopped by the sensing period information setting part in the sensing period; and a sensing period information receiving part configured to receive the sensing period information from a base station of the interfered system. a sensing period information setting part for setting sensing period information that indicates a sensing period for sensing a signal which is sent from a device of the interfered system and received by the wireless terminal device using the shared frequency band; an RF part configured to perform reception processing of a wireless signal via an antenna; a PHY processing part configured to perform reception processing in a physical layer; a MAC processing part configured to perform reception processing in a MAC layer and control the reception timing of reception data; a transmission power controlling part for controlling a transmission power; a sharing condition calculating part for using the sensing result by a sensing part as a basis to determine a sharing condition; and further comprising: the sharing condition containing at least transmission power information as a condition for transmission with use of the shared frequency band; the sensing period information setting part is configured to stop the function of the transmission power controlling part until an end of the sensing period to prohibit transmission; the wireless terminal device further comprising: the sensing part configured to sense the signal from the device of the interfered system in a state where the transmission is stopped by the sensing period information setting part in the sensing period; and a sensing period information receiving part configured to receive the sensing period information from a base station of the interfered system. the sharing condition containing at least transmission power information as a condition for transmission with use of the shared frequency band; the sensing period information setting part is configured to stop the function of the transmission power controlling part until an end of the sensing period to prohibit transmission; the wireless terminal device further comprising: the sensing part configured to sense the signal from the device of the interfered system in a state where the transmission is stopped by the sensing period information setting part in the sensing period; and a sensing period information receiving part configured to receive the sensing period information from a base station of the interfered system. the sensing part configured to sense the signal from the device of the interfered system in a state where the transmission is stopped by the sensing period information setting part in the sensing period; and a sensing period information receiving part configured to receive the sensing period information from a base station of the interfered system.