A receiving device (120; 500) for processing an attention message, the receiving device comprising: one or more processors; memory storing instructions configured to cause the one or more processors to: receive a message via a network, the message being a chat message transmitted from a transmitting device operated by a first user and directed to a second user in a chat room in which the first user and the second user participate; determine that the received message is an attention-specific message specifically for instructing display of an attention indicator in a user interface of the chat room; respond to determining that the received message is an attention-specific message by setting an attention display flag in the memory, the attention display flag being a flag indicating that the attention indicator is to be displayed; and display the attention indicator in the user interface of the chat room based on attention display flag having been set, wherein the message includes an ID of the chat room, an ID of the transmitting device, an ID of the first user, a type indicator indicating a type of the message, a content of the message, and a time of the message, and wherein the determining whether the message is an attention-specification message is based on the content of the message being blank, or the transmission time being an invalid time value. one or more processors; memory storing instructions configured to cause the one or more processors to: receive a message via a network, the message being a chat message transmitted from a transmitting device operated by a first user and directed to a second user in a chat room in which the first user and the second user participate; determine that the received message is an attention-specific message specifically for instructing display of an attention indicator in a user interface of the chat room; respond to determining that the received message is an attention-specific message by setting an attention display flag in the memory, the attention display flag being a flag indicating that the attention indicator is to be displayed; and display the attention indicator in the user interface of the chat room based on attention display flag having been set, wherein the message includes an ID of the chat room, an ID of the transmitting device, an ID of the first user, a type indicator indicating a type of the message, a content of the message, and a time of the message, and wherein the determining whether the message is an attention-specification message is based on the content of the message being blank, or the transmission time being an invalid time value. receive a message via a network, the message being a chat message transmitted from a transmitting device operated by a first user and directed to a second user in a chat room in which the first user and the second user participate; determine that the received message is an attention-specific message specifically for instructing display of an attention indicator in a user interface of the chat room; respond to determining that the received message is an attention-specific message by setting an attention display flag in the memory, the attention display flag being a flag indicating that the attention indicator is to be displayed; and display the attention indicator in the user interface of the chat room based on attention display flag having been set, wherein the message includes an ID of the chat room, an ID of the transmitting device, an ID of the first user, a type indicator indicating a type of the message, a content of the message, and a time of the message, and wherein the determining whether the message is an attention-specification message is based on the content of the message being blank, or the transmission time being an invalid time value.