To provide an existing-in-room confirmation lock device completed only by a lock device, capable of being constituted inexpensively, capable of being easily retrofitted to an existing lock device, allowing an in-home state to be confirmed from the outside, making release operation unnecessary and capable of eliminating an erroneous report at the time of being absent from home.

An existing-in-room confirmation lock device 11 comprises: a locking detection part 13 which is attached to an indoor exposed member 25 of a lock device 23 provided on a door 21 and which detects only locking operation of the lock device 23 performed from the indoor; timer means 15 which starts time measurement in response to the detection of the locking detection part 13 and outputs a time lapse signal after a lapse of a predetermined time; notification means 17 which is provided on an outdoor exposed member of the lock device 23; and control means 19 which drives the notification means 17 by the input of the time lapse signal.