An electrical connection device includes a first connector (C1) having a first housing (10), a second connector (C2) having a second housing (20) for receiving the insertion of the first housing (10), and a connection detecting tool (30). The first housing (10) includes a housing body (12), a lock (14) having a tool restraining portion (14d) and a displacement restricting portion (16) for blocking an insertion allowing displacement of the lock (14). The connection detecting tool (30) is held at an operating position to resiliently deform the displacement restricting portion (16) to allow the insertion allowing displacement. The tool restraining portion (14d) restrains the connection detecting tool (30) at the operating position so as not to be separable while allowing the separation of the connection detecting tool (30) from the operating position as the lock (14) resiliently returns to a lock position.