PURPOSE: To quickly turn a connecting member in lock into an unlocked state by using a card of a simple constitution related with the structure of a card applied for lock for guaranteeing safety for a shopping cart or plural baggage carriers or the like.

CONSTITUTION: A magnet being trigger for turning lock for safety protection into an unlocked state is fixed so as to be movable in the lock so that the lock can be magnetically operated by a card 1, and the card 1 is formed of a magnetic material, for example, metal, or a magnetic area, for example, a metallic foil 2 is formed at one part of the card. Preferably, the magnetic area is provided between two plastic faces. Moreover, the card has a magnetic strip, and the items of information are stored or called through a reading/writing device by this magnetic strip.