A chatbot server that provides an instant messaging service using a virtual chatbot linked to multiple real chatbots includes a receiving unit that receives, from a messenger server, a question message relevant to a service selected from multiple services by a user device and service account information corresponding to the selected service; a derivation unit that derives an answer to the question message using the virtual chatbot corresponding to the service account information; and a transmission unit that transmits the answer to the messenger server, wherein the virtual chatbot transfers the question message to a selected real chatbot of the multiple real chatbots linked to the virtual chatbot, and the selected real chatbot derives the answer to the question message and transfers the answer to the virtual chatbot.