A master device of Profibus DP configured to automatically configure a network by performing a communication with a plurality of slave devices, comprising: a Profibus communication module configured to perform a communication with a plurality of slave devices via Profibus DP protocol; a network configuration information storage configured to store network configuration information; and a Profibus master state machine configured to perform a communication with the plurality of slave devices based on the stored network configuration information; characterized by: a virtual network configuration information storage configured to store in advance virtual network configuration information; and a slave information collector configured to collect actual network information for generating the network configuration information from each of slave devices which are connected to the Profibus communication module, when the network configuration information is not stored in the network configuration information storage or when the network automatic configuration command is inputted, wherein the slave information collector is configured to request the Profibus master state machine to perform a communication with the plurality of slave devices based on the virtual network configuration information stored in the virtual network configuration information storage in order to obtain the actual network information, and the Profibus master state machine is configured to store the obtained actual network information as a network configuration information in the network configuration information storage. a Profibus communication module configured to perform a communication with a plurality of slave devices via Profibus DP protocol; a network configuration information storage configured to store network configuration information; and a Profibus master state machine configured to perform a communication with the plurality of slave devices based on the stored network configuration information; characterized by: a virtual network configuration information storage configured to store in advance virtual network configuration information; and a slave information collector configured to collect actual network information for generating the network configuration information from each of slave devices which are connected to the Profibus communication module, when the network configuration information is not stored in the network configuration information storage or when the network automatic configuration command is inputted, a virtual network configuration information storage configured to store in advance virtual network configuration information; and a slave information collector configured to collect actual network information for generating the network configuration information from each of slave devices which are connected to the Profibus communication module, when the network configuration information is not stored in the network configuration information storage or when the network automatic configuration command is inputted, wherein the slave information collector is configured to request the Profibus master state machine to perform a communication with the plurality of slave devices based on the virtual network configuration information stored in the virtual network configuration information storage in order to obtain the actual network information, and the Profibus master state machine is configured to store the obtained actual network information as a network configuration information in the network configuration information storage.