A terminal mounted in advance on a battery of an instrument that is a management target wirelessly transmits a battery state obtained by detecting an electric property related to a remaining battery amount of the battery and a terminal ID for identifying the terminal, and a management device displays remaining amount information related to the battery remaining amount on a screen based on the terminal ID and the battery state received from the terminal. This allows a user to easily figure out the remaining amount of a battery being used in an existing instrument.