An electronic device testing apparatus with a locking mechanism for locking a press head and a socket plate is provided. When an electronic device is to be tested, a lifting arm is lowered so that a contact portion is in contact with the electronic device, and a locking mechanism is actuated to detain the press head on the socket plate. A pressing force generating device exerts a pressing force onto the electronic device and the socket plate, and at least a portion of a reaction force can be directed back to the locking mechanism. The locking mechanism is adapted to detain the press head on the socket plate. When the pressing force generating device generates a predetermined pressing force to certainly establish electrical connection between the electronic device and the chip socket, the reaction force produced by the chip socket may be distributed over the locking mechanism.