A work machine, comprising: a front implement that includes a boom and an arm rotatably and pivotally supported by a tip end portion of the boom; a first hydraulic actuator configured to drive the boom; a second hydraulic actuator configured to drive the arm; a first operation device configured to command an operation of the first hydraulic actuator; a second operation device configured to command an operation of the second hydraulic actuator; a hydraulic pump configured to supply a hydraulic fluid to the second hydraulic actuator; a regeneration circuit configured to regenerate a return hydraulic fluid from the first hydraulic actuator between the second hydraulic actuator and the hydraulic pump; a discharge circuit configured to discharge the return hydraulic fluid from the first hydraulic actuator to a tank; a regeneration amount regulation device configured to regulate a proportion of a flow rate of the return hydraulic fluid flowing to the regeneration circuit and a flow rate of the return hydraulic fluid flowing to the discharge circuit; and a first operation amount sensor configured to detect an operation amount of the first operation device; characterized by a first speed computing unit configured to compute an actual lowering speed of the boom, and a controller configured to control the regeneration amount regulation device on the basis of the operation amount of the first operation device detected by the first operation amount sensor and the actual lowering speed of the boom computed by the first speed computing unit, wherein the controller includes a regeneration amount regulation device command value computing section configured to compute a lowering speed target value of the boom on the basis of the operation amount of the first operation device detected by the first operation amount sensor (53a, 54a), and compute a command signal to control the regeneration amount regulation device in such a manner that the return hydraulic fluid from the first hydraulic actuator flows more to the discharge circuit than to the regeneration circuit in a case where the actual lowering speed of the boom computed by the first speed computing unit is lower than the lowering speed target value of the boom, compared with cases other than the case. a front implement that includes a boom and an arm rotatably and pivotally supported by a tip end portion of the boom; a first hydraulic actuator configured to drive the boom; a second hydraulic actuator configured to drive the arm; a first operation device configured to command an operation of the first hydraulic actuator; a second operation device configured to command an operation of the second hydraulic actuator; a hydraulic pump configured to supply a hydraulic fluid to the second hydraulic actuator; a regeneration circuit configured to regenerate a return hydraulic fluid from the first hydraulic actuator between the second hydraulic actuator and the hydraulic pump; a discharge circuit configured to discharge the return hydraulic fluid from the first hydraulic actuator to a tank; a regeneration amount regulation device configured to regulate a proportion of a flow rate of the return hydraulic fluid flowing to the regeneration circuit and a flow rate of the return hydraulic fluid flowing to the discharge circuit; and a first operation amount sensor configured to detect an operation amount of the first operation device; characterized by a first speed computing unit configured to compute an actual lowering speed of the boom, and a controller configured to control the regeneration amount regulation device on the basis of the operation amount of the first operation device detected by the first operation amount sensor and the actual lowering speed of the boom computed by the first speed computing unit, wherein the controller includes a regeneration amount regulation device command value computing section configured to compute a lowering speed target value of the boom on the basis of the operation amount of the first operation device detected by the first operation amount sensor (53a, 54a), and compute a command signal to control the regeneration amount regulation device in such a manner that the return hydraulic fluid from the first hydraulic actuator flows more to the discharge circuit than to the regeneration circuit in a case where the actual lowering speed of the boom computed by the first speed computing unit is lower than the lowering speed target value of the boom, compared with cases other than the case.