Provided is a construction machine allowing regeneration of a return hydraulic fluid at the time of both a boom raising operation and a boom lowering operation with a small number of valves, making it possible to secure a satisfactory operability at the time of both the boom raising operation and the boom lowering operation.The construction machine includes: a first hydraulic actuator; a second hydraulic actuator; a tank; and a first hydraulic pump supplying a hydraulic fluid to the second hydraulic actuator, the construction machine further including: a return hydraulic fluid selection device selecting a supply source of a return hydraulic fluid generated at a time of a raising operation or a lowering operation of the first hydraulic actuator and discharging the return hydraulic fluid; a regeneration line supplying the hydraulic fluid discharged from the return hydraulic fluid selection device to a portion between the second hydraulic actuator and the first hydraulic pump to regenerate the hydraulic fluid; a discharge line discharging the hydraulic fluid discharged from the return hydraulic fluid selection device to the tank; and a regeneration/discharge flow rate adjustment device capable of adjusting a flow rate of the hydraulic fluid flowing through the regeneration line and a flow rate of the hydraulic fluid flowing through the discharge line.