A bypass line (35) having one end side connected to a pilot delivery line (23) between a pilot pump (16) and a throttle (32) and the other end side connected to the pilot delivery line (23) between a check valve (33) and a pressure reducing valve type pilot valve (25) so as to bypass the throttle (32), a gate lock valve (27), and the check valve (33) provided in order from a pilot pump (16) is provided in the pilot delivery line (23). A lock switching valve (36) shutting down a flow of a pilot pressure oil from the pilot pump (16) through the bypass line (35) at a normal time and allowing the flow of the pilot pressure oil through the bypass line (35) when a pressure generated in the pilot delivery line (23) exceeds a predetermined pressure between the gate lock valve (27) and the check valve (33) is provided in the bypass line (35).