A steering control device that controls a steering device that assists steering of a vehicle and that includes a synchronous motor that generates assist torque and a power conversion circuit that applies a voltage to the synchronous motor, the steering control device comprising a sensorless processing circuit which controls the assist torque of the synchronous motor in the case where an abnormality is caused in a rotational angle sensor which detects a rotational angle of the rotary shaft of the synchronous motor, said sensorless processing circuit comprising: a current control processing circuit that manipulates the voltage, which is applied to the synchronous motor by the power conversion circuit, in order to control a current (iγ, iδ) that flows through the synchronous motor to a command value (iγ*, iδ*); a control angle manipulation processing circuit (M52, M54a, M54b) that manipulates a control angle (θc) that is to be input to a current feedback controller and determines a phase of the command value (iγ*, iδ*) in order to control a detected value of steering torque (Trqs), which is torque input to a steering member, to target torque (Trqs*) through feedback control; and a torque-based guarding processing circuit that performs a guarding process such that an update amount (Δθc2) for the control angle (θc) determined by the control angle manipulation processing circuit is equal to or less than a torque-based upper-limit guard value (ΔMAX), which is an upper-limit guard value for a magnitude of the update amount (Δθc) in a rotational direction of the synchronous motor that matches the detected value (Trqs), and equal to or more than a torque-based lower-limit guard value (ΔMIN), which is a lower-limit guard value for the magnitude of the update amount (Δθc) in the rotational direction of the synchronous motor that matches the detected value (Trqs), characterized in that the torque-based guarding processing circuit includes a contraction processing circuit (CPU 52) that gradually contracts an allowable range of the update amount (Δθc) determined by the torque-based upper-limit guard value (ΔMAX) and the torque-based lower-limit guard value (ΔMIN) using, as a condition, at least one of a state in which the magnitude of the update amount (Δθc2) is more than the torque-based upper-limit guard value (ΔMAX) and a state in which the magnitude of the update amount (Δθc2) is less than the torque-based lower-limit guard value (ΔMIN). a current control processing circuit that manipulates the voltage, which is applied to the synchronous motor by the power conversion circuit, in order to control a current (iγ, iδ) that flows through the synchronous motor to a command value (iγ*, iδ*); a control angle manipulation processing circuit (M52, M54a, M54b) that manipulates a control angle (θc) that is to be input to a current feedback controller and determines a phase of the command value (iγ*, iδ*) in order to control a detected value of steering torque (Trqs), which is torque input to a steering member, to target torque (Trqs*) through feedback control; and a torque-based guarding processing circuit that performs a guarding process such that an update amount (Δθc2) for the control angle (θc) determined by the control angle manipulation processing circuit is equal to or less than a torque-based upper-limit guard value (ΔMAX), which is an upper-limit guard value for a magnitude of the update amount (Δθc) in a rotational direction of the synchronous motor that matches the detected value (Trqs), and equal to or more than a torque-based lower-limit guard value (ΔMIN), which is a lower-limit guard value for the magnitude of the update amount (Δθc) in the rotational direction of the synchronous motor that matches the detected value (Trqs), characterized in that the torque-based guarding processing circuit includes a contraction processing circuit (CPU 52) that gradually contracts an allowable range of the update amount (Δθc) determined by the torque-based upper-limit guard value (ΔMAX) and the torque-based lower-limit guard value (ΔMIN) using, as a condition, at least one of a state in which the magnitude of the update amount (Δθc2) is more than the torque-based upper-limit guard value (ΔMAX) and a state in which the magnitude of the update amount (Δθc2) is less than the torque-based lower-limit guard value (ΔMIN).