A deceleration device includes a driving device and a transmission assembly. The transmission assembly includes a driving member, a first active subassembly, a second active subassembly, a first transmission member, a second transmission member and two regulatory mechanisms. The driving member is connected to the driving device. The first transmission member connects the driving member to the first active subassembly, and is driven by the driving device, and rotates the first active subassembly. The second transmission member connects the first active subassembly to the second active subassembly, and is driven by the first active subassembly, and rotates the second active subassembly. The two regulatory mechanisms elastically resist the first transmission member and the second transmission member, respectively.