A sensor node, comprising: a) a sensor adapted to collect sensor information at a location where the sensor is installed, the sensor being adapted to collect the sensor information in autonomous timing; b) a control unit connected to the sensor, the control unit being adapted to execute calculation processing of the sensor information collected by the sensor; c) a memory connected to the control unit; d) a wireless transmission/reception unit connected to the control unit; e) an antenna connected to the wireless transmission/reception unit, the antenna being adapted to wirelessly transmit first wireless transmission data containing the sensor information or a result of the calculation processing of the sensor information and to receive second wireless transmission data from a host, said host being configured to collect the first wireless transmission data and to control the sensor node; f) a power supply unit connected to the control unit; and g) a timer connected to the control unit, the timer being adapted to supply a timer count value used for a timing control of the sensor node, wherein the sensor node is adapted to, when the first wireless transmission data is transmitted from the antenna to the host, h)-provide, to the host, after transmission of the first wireless transmission data, a reception window indicating a predetermined time period during which the sensor node can receive the second wireless transmission data from the host, and i) if no second wireless transmission data is transmitted from the host to the sensor node during the reception window, or if the second wireless transmission data transmitted from the host to the sensor node is a control signal, close the reception window, shift to a sleep mode,=wherein a period of the sleep mode is determined on the basis of the timer count value supplied from the timer, and, after expiration of said period, initiate a next transmission of the next first wireless transmission data, wherein j) the wireless transmission/reception unit comprises a receiving unit configured to receive an instruction to change a communication rate from the host, and k) the control unit comprises a slave rate unit configured to instruct the change of the communication rate with respect to the host side in response to the instruction from the host received in the receiving unit, wherein the communication rate is the bit rate for the data transmission from the sensor node to the host. a) a sensor adapted to collect sensor information at a location where the sensor is installed, the sensor being adapted to collect the sensor information in autonomous timing; b) a control unit connected to the sensor, the control unit being adapted to execute calculation processing of the sensor information collected by the sensor; c) a memory connected to the control unit; d) a wireless transmission/reception unit connected to the control unit; e) an antenna connected to the wireless transmission/reception unit, the antenna being adapted to wirelessly transmit first wireless transmission data containing the sensor information or a result of the calculation processing of the sensor information and to receive second wireless transmission data from a host, said host being configured to collect the first wireless transmission data and to control the sensor node; f) a power supply unit connected to the control unit; and g) a timer connected to the control unit, the timer being adapted to supply a timer count value used for a timing control of the sensor node, h)-provide, to the host, after transmission of the first wireless transmission data, a reception window indicating a predetermined time period during which the sensor node can receive the second wireless transmission data from the host, and i) if no second wireless transmission data is transmitted from the host to the sensor node during the reception window, or if the second wireless transmission data transmitted from the host to the sensor node is a control signal, close the reception window, shift to a sleep mode,=wherein a period of the sleep mode is determined on the basis of the timer count value supplied from the timer, and, after expiration of said period, initiate a next transmission of the next first wireless transmission data, wherein j) the wireless transmission/reception unit comprises a receiving unit configured to receive an instruction to change a communication rate from the host, and k) the control unit comprises a slave rate unit configured to instruct the change of the communication rate with respect to the host side in response to the instruction from the host received in the receiving unit,