To provide a compact locking device for opening/closing body for building having high crime prevention property, although it has a simple configuration.

This locking device locks an opening/closing body for opening and closing an opening part of a building in a closed condition. The locking device is composed of lock receiver parts 6, 6 and a first locking part J1 and a second locking part J2 which are changed into a locking condition in which they are engaged with the lock receive parts 6, 6 and an unlocking condition in which the engagement is released. The change of condition of each locking part J1, J2 from the locking condition into the unlocking condition is performed only based on only simultaneous unlocking operation of each locking part J1, J2.