A construction machine comprising: a track structure; a swing structure provided on the track structure in a swingable manner; a swing motor (25,27) that drives and swings the swing structure; a boom connected to the swing structure; a boom cylinder that moves the boom vertically; a swing operation system that instructs a swing operation of the swing structure; a boom operation system that instructs a vertical movement of the boom; a detector (74d,74e) that detects a state quantity varying according to a load on the boom cylinder; and a controller that reduces a swing speed of the swing structure according to a signal from the detector (74d,74e) with respect to a reference swing speed according to a signal of the swing operation, while signals of the swing operation by the swing operation system and a boom raising operation by the boom operation system are being inputted, characterized in that the controller includes: a boom speed reduction calculation section configured to calculate a boom speed reduction amount ΔR with respect to a reference boom raising speed Rs that is suited to an operation amount of the boom operation system on the basis of the signal from the detector (74d,74e); a swing speed reduction amount calculation section configured to calculate a swing speed reduction amount ΔS with respect to a reference swing speed Ss that is suited to an operation amount of the swing operation system on the basis of the operation amount of the swing operation system and the boom speed reduction amount ΔR; and a torque command calculation section configured to calculate and output a swing motor torque command for generating the swing speed reduction amount ΔS on the basis of swing torque of the swing motor (25,27) and the swing speed reduction amount ΔS, and wherein the swing speed reduction amount calculation section calculates the swing speed reduction amount ΔS such that the relation of (Rs - ΔR)/(Ss - ΔS) = Rs/Ss is established. a track structure; a swing structure provided on the track structure in a swingable manner; a swing motor (25,27) that drives and swings the swing structure; a boom connected to the swing structure; a boom cylinder that moves the boom vertically; a swing operation system that instructs a swing operation of the swing structure; a boom operation system that instructs a vertical movement of the boom; a detector (74d,74e) that detects a state quantity varying according to a load on the boom cylinder; and a controller that reduces a swing speed of the swing structure according to a signal from the detector (74d,74e) with respect to a reference swing speed according to a signal of the swing operation, while signals of the swing operation by the swing operation system and a boom raising operation by the boom operation system are being inputted, a boom speed reduction calculation section configured to calculate a boom speed reduction amount ΔR with respect to a reference boom raising speed Rs that is suited to an operation amount of the boom operation system on the basis of the signal from the detector (74d,74e); a swing speed reduction amount calculation section configured to calculate a swing speed reduction amount ΔS with respect to a reference swing speed Ss that is suited to an operation amount of the swing operation system on the basis of the operation amount of the swing operation system and the boom speed reduction amount ΔR; and a torque command calculation section configured to calculate and output a swing motor torque command for generating the swing speed reduction amount ΔS on the basis of swing torque of the swing motor (25,27) and the swing speed reduction amount ΔS, and wherein the swing speed reduction amount calculation section calculates the swing speed reduction amount ΔS such that the relation of (Rs - ΔR)/(Ss - ΔS) = Rs/Ss is established.