A control device for a turbocharger of an engine, the turbocharger comprising an exhaust gas turbine driven by an exhaust gas of the engine, a compressor which supplies fresh air to the engine under a supercharging pressure according to a rotation of the exhaust gas turbine, and a mechanism (53, 54, 56, 59) which adjusts a flowpath cross-sectional area of the exhaust gas led to the exhaust gas turbine, the control device comprising: a running state detection sensor which detects a running state of the engine, wherein the running state detection sensor comprises a sensor which detects a rotation speed of the engine and a sensor which detects a load of the engine; a sensor which detects an intake air amount of the engine; and a controller functioning to: set an open loop control value of the flowpath cross-sectional area based on the running state; set a target intake air amount of the engine based on the running state (S115, S116); calculate a processing value wherein predetermined smoothing is performed on the target intake air amount; calculate a feedback correction amount which makes the intake air amount coincide with the processing value; control the exhaust gas flowpath cross-sectional area of the mechanism (53, 54, 56) based on the open loop control value and feedback correction amount; and prohibit calculation of the feedback correction amount or perform control of the exhaust gas flowpath cross-sectional area adjustment mechanism (53, 54, 56) so that the exhaust gas flowpath cross-sectional area is less than a predetermined value, when the rotation speed is smaller than a predetermined speed and the load is smaller than a predetermined load (S341, S346, S352, S353). a running state detection sensor which detects a running state of the engine, wherein the running state detection sensor comprises a sensor which detects a rotation speed of the engine and a sensor which detects a load of the engine; a sensor which detects an intake air amount of the engine; and a controller functioning to: set an open loop control value of the flowpath cross-sectional area based on the running state; set a target intake air amount of the engine based on the running state (S115, S116); calculate a processing value wherein predetermined smoothing is performed on the target intake air amount; calculate a feedback correction amount which makes the intake air amount coincide with the processing value; control the exhaust gas flowpath cross-sectional area of the mechanism (53, 54, 56) based on the open loop control value and feedback correction amount; and prohibit calculation of the feedback correction amount or perform control of the exhaust gas flowpath cross-sectional area adjustment mechanism (53, 54, 56) so that the exhaust gas flowpath cross-sectional area is less than a predetermined value, when the rotation speed is smaller than a predetermined speed and the load is smaller than a predetermined load (S341, S346, S352, S353). set an open loop control value of the flowpath cross-sectional area based on the running state; set a target intake air amount of the engine based on the running state (S115, S116); calculate a processing value wherein predetermined smoothing is performed on the target intake air amount; calculate a feedback correction amount which makes the intake air amount coincide with the processing value; control the exhaust gas flowpath cross-sectional area of the mechanism (53, 54, 56) based on the open loop control value and feedback correction amount; and prohibit calculation of the feedback correction amount or perform control of the exhaust gas flowpath cross-sectional area adjustment mechanism (53, 54, 56) so that the exhaust gas flowpath cross-sectional area is less than a predetermined value, when the rotation speed is smaller than a predetermined speed and the load is smaller than a predetermined load (S341, S346, S352, S353).