Disclosed is an internal combustion engine control device that is capable of accurately estimating a turbine flow rate during a transient operation of an internal combustion engine with a turbocharger having a WGV. Steps are performed to acquire an exhaust gas flow rate mcyl (=mB), a WGV opening WG (=X), and a turbine rotation speed Ntb (=Na) during the transient operation of the internal combustion engine. Steps are then performed to calculate the turbine flow rate (=mtA) and exhaust gas flow rate mcyl (=mA), which prevail when the turbine rotation speed Ntb and WGV opening WG acquired during the transient operation are achieved during a steady operation. Next, a step is performed to calculate the turbine flow rate (=mtB) during the transient operation by applying the flow rate ratio of mtA to mA to the exhaust gas flow rate mcyl during the transient operation. Preferably, the turbine rotation speed Ntb during an Ntb transient operation is estimated by using a turbine flow rate change amount Δmt (=mtB−mtA) during the transient operation.