A bicycle rental system, comprising: a fixed dock; a rental bicycle including a locking apparatus, a bicycle locking device, and a controlling apparatus, wherein the controlling apparatus includes a processor, to which a display, a code generating module, a transceiver module, and a positioning module are electrically connected; a mobile device installed with a predetermined application; and a control system receiving signals from the transceiver module of the rental bicycle and transmitting signals to the transceiver module of the rental bicycle; wherein when a user rents the rental bicycle, the code generating module generates a rental code by a control of the processor, and the user operates the mobile device to scan the rental code; and then the mobile device transmits the rental code and a user data to the control system whereby the user is able to ride the rental bicycle; wherein the rental bicycle is returned through a return process without dock or a return process with dock; wherein in the return process with dock, a user locks the rental bicycle to the dock, and then the transceiver module of the rental bicycle is controlled by the processor to transmit a return signal and a position data to the control system to complete the return process with dock; the bicycle rental system being characterised in that: wherein in the return process without dock, a user engages the bicycle locking device with the locking apparatus to lock the rental bicycle, and then the transceiver module of the rental bicycle is controlled by the processor to transmit a return signal and a position data to the control system to complete the return process without dock; the locking apparatus of the rental bicycle has a locking member and a locking board; the locking member has a movable latch, and the locking board has a slot; the latch is driven to engage the slot when a handlebar of the rental bicycle is turned to a predetermined angle to lock the rental bicycle; and the locking member has a first sensing member, and the bicycle locking device has a second sensing member; the first sensing member detects the second sensing member when the bicycle locking device engages the locking member, and then the transceiver module transmits the return signal to the control system when the first sensing member detects the second sensing member. a fixed dock; a rental bicycle including a locking apparatus, a bicycle locking device, and a controlling apparatus, wherein the controlling apparatus includes a processor, to which a display, a code generating module, a transceiver module, and a positioning module are electrically connected; a mobile device installed with a predetermined application; and a control system receiving signals from the transceiver module of the rental bicycle and transmitting signals to the transceiver module of the rental bicycle; wherein when a user rents the rental bicycle, the code generating module generates a rental code by a control of the processor, and the user operates the mobile device to scan the rental code; and then the mobile device transmits the rental code and a user data to the control system whereby the user is able to ride the rental bicycle; wherein the rental bicycle is returned through a return process without dock or a return process with dock; wherein in the return process with dock, a user locks the rental bicycle to the dock, and then the transceiver module of the rental bicycle is controlled by the processor to transmit a return signal and a position data to the control system to complete the return process with dock; the bicycle rental system being characterised in that: wherein in the return process without dock, a user engages the bicycle locking device with the locking apparatus to lock the rental bicycle, and then the transceiver module of the rental bicycle is controlled by the processor to transmit a return signal and a position data to the control system to complete the return process without dock; the locking apparatus of the rental bicycle has a locking member and a locking board; the locking member has a movable latch, and the locking board has a slot; the latch is driven to engage the slot when a handlebar of the rental bicycle is turned to a predetermined angle to lock the rental bicycle; and the locking member has a first sensing member, and the bicycle locking device has a second sensing member; the first sensing member detects the second sensing member when the bicycle locking device engages the locking member, and then the transceiver module transmits the return signal to the control system when the first sensing member detects the second sensing member. wherein in the return process without dock, a user engages the bicycle locking device with the locking apparatus to lock the rental bicycle, and then the transceiver module of the rental bicycle is controlled by the processor to transmit a return signal and a position data to the control system to complete the return process without dock; the locking apparatus of the rental bicycle has a locking member and a locking board; the locking member has a movable latch, and the locking board has a slot; the latch is driven to engage the slot when a handlebar of the rental bicycle is turned to a predetermined angle to lock the rental bicycle; and the locking member has a first sensing member, and the bicycle locking device has a second sensing member; the first sensing member detects the second sensing member when the bicycle locking device engages the locking member, and then the transceiver module transmits the return signal to the control system when the first sensing member detects the second sensing member.