A hydraulic control device for a work machine, comprising: a hydraulic pump driven by an engine; a traveling motor that generates a driving force for traveling of the work machine by hydraulic oil supplied from the hydraulic pump; an operating lever for operating a work device, which can be provided in a cab of the work machine; a first clutch and a second clutch having different transmission gear ratio, which function as a park braking device for parking the work machine; a hydraulic pressure source which generates pilot pressure for driving the work device and supplies the hydraulic oil to the first clutch and the second clutch; characterised by an electromagnetic changeover valve which supplies the hydraulic oil supplied from the hydraulic pressure source to one of the first clutch and the second clutch; a gate lock changeover valve which is changed over between a lock position for blocking the pilot pressure and a lock release position for communicating the pilot pressure; and a controller adapted to control the gate lock changeover valve based on signals output from a work brake switch for commanding operation or release of a work brake and a gate lock lever that can be provided within the cab of the work machine, wherein the electromagnetic changeover valve includes a changeover position for supplying the hydraulic oil to both the first clutch and the second clutch, and the controller is further adapted to, in a state where the work brake switch is operated and one of the first clutch and the second clutch is engaged, when the gate lock lever is operated to the lock position, cause the electromagnetic changeover valve to be changed over to the changeover position, and cause the park braking device to be activated by the work machine such that both the first clutch and the second clutch are engaged by the hydraulic oil supplied from the hydraulic pressure source. a hydraulic pump driven by an engine; a traveling motor that generates a driving force for traveling of the work machine by hydraulic oil supplied from the hydraulic pump; an operating lever for operating a work device, which can be provided in a cab of the work machine; a first clutch and a second clutch having different transmission gear ratio, which function as a park braking device for parking the work machine; a hydraulic pressure source which generates pilot pressure for driving the work device and supplies the hydraulic oil to the first clutch and the second clutch; characterised by an electromagnetic changeover valve which supplies the hydraulic oil supplied from the hydraulic pressure source to one of the first clutch and the second clutch; a gate lock changeover valve which is changed over between a lock position for blocking the pilot pressure and a lock release position for communicating the pilot pressure; and a controller adapted to control the gate lock changeover valve based on signals output from a work brake switch for commanding operation or release of a work brake and a gate lock lever that can be provided within the cab of the work machine, wherein the electromagnetic changeover valve includes a changeover position for supplying the hydraulic oil to both the first clutch and the second clutch, and the controller is further adapted to, in a state where the work brake switch is operated and one of the first clutch and the second clutch is engaged, when the gate lock lever is operated to the lock position, cause the electromagnetic changeover valve to be changed over to the changeover position, and cause the park braking device to be activated by the work machine such that both the first clutch and the second clutch are engaged by the hydraulic oil supplied from the hydraulic pressure source.