A chatbot server that provides an instant messaging service using a relay chatbot linked to multiple chatbots includes a receiving unit that receives, from a messenger server, a question message relevant to a service selected from multiple services and service account information corresponding to the selected service; a derivation unit that derives an answer to the question message using the relay chatbot corresponding to the service account information; and a transmission unit that transmits the answer to the messenger server, wherein the relay chatbot relays a user device to the multiple chatbots linked to the relay chatbot to derive the answer through at least one of the multiple chatbots.