To provide a gas appliance monitor capable of carrying out easily data transfer work after finishing replacement work for a gas meter.

The gas meter 2 has a flow measuring means 12, a registration storage means 16 for storing a use flow rate pattern, an appliance determination means 24 for comparing a measured flow rate value with the flow rate pattern to judge a used appliance, an appliance-by-appliance monitoring means 21 for monitoring a using situation by classification in correspondence to provided service, a data storage means 22 for storing the registration storage means 16 and the appliance-by-appliance monitoring means 21 in one storage medium, a storage part 23 for storing removably the data storage means 22, an opening and closing detecting means 29 for detecting opening and closing of a lid for covering the storage part 23, a meter side radio communication means 25 for transmitting data, an authentication code collating means 26 for executing collation with an authentication code to judge the propriety of authentication, and an alarm means 27 for processing a detection signal from the opening and closing detecting means 29, as invalid or valid one, based on a collation result.