The invention provides a branch well sidetrack drilling device, which comprises a pipe column and drill pipes, wherein the pipe column is used for being released to a branch well reservoir; at least two drill-out holes in different directions are formed in the side part of a pipe body; a liquid inlet used for receiving liquid is formed in the top of the pipe column; the drill pipes are arranged in the pipe body; one ends of the drill pipes extend to the outer side from the drill-out holes; each drill-out hole is provided with at most one drill pipe; and the drill pipes are constructed into a state of being capable of propelling towards the branch well reservoir under the pressure effect of liquid injected into the pipe column in the branch well sidetrack drilling process. The simultaneous sidetrack drilling of at least two branch wells can be realized; at least two oil gas passages are formed after the once sidetrack drilling; the reservoir can be communicated to the maximum degree; the device can be applied to various reservoirs, and is particularly applicable to a carbonatite reservoir and a sandrock thin interbed reservoir.