A control system design assist device for assisting design of a control system that controls an amount of controlling a control object to a target value, the design assist device comprising: a response prediction formula generation unit configured to, on the basis of a response waveform of the control amount when an operation amount of the control object is changed, a sequence of control timings at which a target deviation, which is a differential between the target value and the control amount, is evaluated, and a sequence of operation timings at which the operation amount is changed, to generate a response prediction formula predicting a variation value of the control amount from an initial value at each control timing included in the sequence of control timings, by using an amount of change of the operation amount at each operation timing included in the sequence of operation timings; an evaluation formula generation unit configured to generate a first evaluation formula that expresses the target deviation at each of the control timings, as a logical formula, on the basis of the response prediction formula and a current value of the target deviation, and also generates a second evaluation formula that expresses a constraint condition for an amount of change of the operation amount (Δu) at each of the operation timings, as a logical formula, and a third evaluation formula that expresses a constraint condition for the target deviation at each of the control timings, as a logical formula; a first-order predicate logical formula conversion unit configured to convert a formula, deriving a logical product of the first to third evaluation formulas, into a first first-order predicate logical formula; a quantifier eliminating unit configured to eliminate variables to which a quantifier has been attached in the first first-order predicate logical formula and to generate a control logical formula (φ0(e0,Δu0)) indicating a relationship between the current value of the target deviation and the change amount of the operation amount (Δu), a display unit, which is adapted to display a region in which the control logical formula is established, on a graph, wherein the first-order predicate logical formula conversion unit is configured to convert a formula deriving a logical product of the first to third evaluation formulas, into a first first-order predicate logical formula in which the quantifier is attached to variables other than the current value of the target deviation and the change amount of the operation amount (Δu) at a first operation timing; and the quantifier eliminating unit is configured to eliminate variables to which the quantifier has been attached in the first first-order predicate logical formula and to generate the control logical formula indicating a relationship between the current value of the target deviation and the change amount of the operation amount (Δu) at the first operation timing. a response prediction formula generation unit configured to, on the basis of a response waveform of the control amount when an operation amount of the control object is changed, a sequence of control timings at which a target deviation, which is a differential between the target value and the control amount, is evaluated, and a sequence of operation timings at which the operation amount is changed, to generate a response prediction formula predicting a variation value of the control amount from an initial value at each control timing included in the sequence of control timings, by using an amount of change of the operation amount at each operation timing included in the sequence of operation timings; an evaluation formula generation unit configured to generate a first evaluation formula that expresses the target deviation at each of the control timings, as a logical formula, on the basis of the response prediction formula and a current value of the target deviation, and also generates a second evaluation formula that expresses a constraint condition for an amount of change of the operation amount (Δu) at each of the operation timings, as a logical formula, and a third evaluation formula that expresses a constraint condition for the target deviation at each of the control timings, as a logical formula; a first-order predicate logical formula conversion unit configured to convert a formula, deriving a logical product of the first to third evaluation formulas, into a first first-order predicate logical formula; a quantifier eliminating unit configured to eliminate variables to which a quantifier has been attached in the first first-order predicate logical formula and to generate a control logical formula (φ0(e0,Δu0)) indicating a relationship between the current value of the target deviation and the change amount of the operation amount (Δu), a display unit, which is adapted to display a region in which the control logical formula is established, on a graph, wherein the first-order predicate logical formula conversion unit is configured to convert a formula deriving a logical product of the first to third evaluation formulas, into a first first-order predicate logical formula in which the quantifier is attached to variables other than the current value of the target deviation and the change amount of the operation amount (Δu) at a first operation timing; and the quantifier eliminating unit is configured to eliminate variables to which the quantifier has been attached in the first first-order predicate logical formula and to generate the control logical formula indicating a relationship between the current value of the target deviation and the change amount of the operation amount (Δu) at the first operation timing.