A wireless communication system in which wireless communication can be performed via a wireless communication network, the wireless communication system comprising: a wireless access point device configured to operate by using power supplied via a two-wire cable and to perform wireless communication with wireless field devices (11a to 11c) via the wireless communication network; and a conversion device connected to the two-wire cable and to a control unit configured to control the wireless field devices (11a to 11c), the conversion device being configured to supply power to the wireless access point device via the two-wire cable, and to perform conversions between communication signals, which are input and output from the control unit, and communication signals, which are transmitted and received via the two-wire cable, characterized in that the wireless access point device is configured to perform communication with the conversion device via the two-wire cable, the conversion device is configured to transmit to the wireless access point device via the two-wire cable first time data that shows the time when the conversion device delivers a synchronization signal transmitted to the wireless access point device to the two-wire cable, and second time data that shows the time when the conversion device receives a synchronization signal from the wireless access point device that was transmitted via the two-wire cable, and the wireless access point device is configured to determine a time differential between times managed by the conversion device and times managed by the wireless access point device and to correct times managed by a time management unit of the wireless access point device such that the time differential is zero by using the time when the wireless access point device receives said synchronization signal from the conversion device that was transmitted via the two-wire cable, the time when the wireless access point device delivers said synchronization signal to be transmitted to the conversion device to the two-wire cable, and the times shown by the first time data and second time data. a wireless access point device configured to operate by using power supplied via a two-wire cable and to perform wireless communication with wireless field devices (11a to 11c) via the wireless communication network; and a conversion device connected to the two-wire cable and to a control unit configured to control the wireless field devices (11a to 11c), the conversion device being configured to supply power to the wireless access point device via the two-wire cable, and to perform conversions between communication signals, which are input and output from the control unit, and communication signals, which are transmitted and received via the two-wire cable, characterized in that the wireless access point device is configured to perform communication with the conversion device via the two-wire cable, the conversion device is configured to transmit to the wireless access point device via the two-wire cable first time data that shows the time when the conversion device delivers a synchronization signal transmitted to the wireless access point device to the two-wire cable, and second time data that shows the time when the conversion device receives a synchronization signal from the wireless access point device that was transmitted via the two-wire cable, and the wireless access point device is configured to determine a time differential between times managed by the conversion device and times managed by the wireless access point device and to correct times managed by a time management unit of the wireless access point device such that the time differential is zero by using the time when the wireless access point device receives said synchronization signal from the conversion device that was transmitted via the two-wire cable, the time when the wireless access point device delivers said synchronization signal to be transmitted to the conversion device to the two-wire cable, and the times shown by the first time data and second time data.