A valve characteristic controller for an internal combustion engine, the controller comprising: a hydraulic pressure pump driven by the engine; a varying mechanism which varies a valve target characteristic value of a valve in the engine based on hydraulic pressure of a hydraulic oil supplied from the hydraulic pressure pump; and a control unit which drives the varying mechanism and controls the valve target characteristic value of the valve to be a target value, in which the control unit includes: a storage which stores computation maps used to calculate the target value for the valve target characteristic value based on a plurality of engine control values including an engine speed; and a detector which detects a temperature of the hydraulic oil; characterized in that the computation maps include a first map and a second map setting the relationship of the valve target characteristic value with respect to the engine control values, with a varying amount of the valve characteristic amount corresponding to a change in the engine control value in a low speed range of the engine speed being set to be smaller in the second map than the first map; and the control unit switches the computation maps from the first map to the second map when the detected temperature of the hydraulic oil is higher than a reference oil temperature. a hydraulic pressure pump driven by the engine; a varying mechanism which varies a valve target characteristic value of a valve in the engine based on hydraulic pressure of a hydraulic oil supplied from the hydraulic pressure pump; and a control unit which drives the varying mechanism and controls the valve target characteristic value of the valve to be a target value, in which the control unit includes: a storage which stores computation maps used to calculate the target value for the valve target characteristic value based on a plurality of engine control values including an engine speed; and a detector which detects a temperature of the hydraulic oil; characterized in that the computation maps include a first map and a second map setting the relationship of the valve target characteristic value with respect to the engine control values, with a varying amount of the valve characteristic amount corresponding to a change in the engine control value in a low speed range of the engine speed being set to be smaller in the second map than the first map; and the control unit switches the computation maps from the first map to the second map when the detected temperature of the hydraulic oil is higher than a reference oil temperature. a storage which stores computation maps used to calculate the target value for the valve target characteristic value based on a plurality of engine control values including an engine speed; and a detector which detects a temperature of the hydraulic oil; characterized in that the computation maps include a first map and a second map setting the relationship of the valve target characteristic value with respect to the engine control values, with a varying amount of the valve characteristic amount corresponding to a change in the engine control value in a low speed range of the engine speed being set to be smaller in the second map than the first map; and the control unit switches the computation maps from the first map to the second map when the detected temperature of the hydraulic oil is higher than a reference oil temperature.