To provide an auxiliary lock device and a crime prevention door system allowing a resident to confirm visitor's face while a door is half-opened and open the door easily when unlocking.

This crime prevention door system 10 includes a main locking device 30 for locking the door 20 and the auxiliary lock device 40. The auxiliary lock device 40 has an electromagnet 50, a driving means 60, an unlocking means 70, a time counting means 80, and a control means 90. The electromagnet 50 is stored in a metallic case 52 having a circular cylindrical shape and is supported to move in the direction for opening the door by only the predetermined distance. A calling means 100 outputs a call signal when operated by a visitor. The control means 90 supplies electric power to the electromagnet 50 through the driving means 60 by the call signals to attract the door 20. The door 20 is opened up to the electromagnet 50 movable distance, and its opening operation is regulated at a position where it is half-opened. When the unlocking means 70 is operated to unlock the door after confirming visitor's face, power supply to the electromagnet 50 is stopped to unlock the auxiliary lock device 40.