A hydraulic fluid supply device, comprising: an adjustable-speed motor; a variable-volume pump which is driven by the adjustable-speed motor and ejects hydraulic fluid; an electric motor control unit which controls the adjustable-speed motor so as to achieve an intended rotation speed; and a pump control unit comprising an operation member (372, 373) which is moved by a pressure of hydraulic fluid ejected from the variable-volume pump, and which increases/decreases the ejection volume of the variable-volume pump; an elastic member which biases the operation member (372, 373) in a direction against the pressure of hydraulic fluid acting on the operation member (372, 373); the pump control unit being configured to control the variable-volume pump so that the ejection volume of the variable-volume pump equals a first ejection volume (Dmax) while the ejection pressure of the variable-volume pump is lower than a predetermined pressure, and that the ejection volume of the variable-volume pump equals a second ejection volume when the ejection pressure of the variable-volume pump reaches the predetermined pressure, the second ejection volume being smaller than the first ejection volume (Dmax), and further comprising a switch valve provided between the variable-volume pump and the operation member (372, 373), which valve is switched to a first switch position so as to block a connection to a passage communicating the variable-volume pump with the operation member (372, 373), or a second switch position so as to communicate the variable-volume pump with the operation member (372, 373), the switch valve being held in the first switch position when the ejection pressure of the variable-volume pump is lower than the predetermined pressure and switched to the second switch position when the ejection pressure of the variable-volume pump reaches the predetermined pressure characterized in that the pump control unit (14, 300, 400) includes a pressure adjustment unit provided between the variable-volume pump and the operation member (72, 73; 372, 373), which adjusts the pressure of hydraulic fluid from the variable-volume pump acting on the operation member. an adjustable-speed motor; a variable-volume pump which is driven by the adjustable-speed motor and ejects hydraulic fluid; an electric motor control unit which controls the adjustable-speed motor so as to achieve an intended rotation speed; and a pump control unit comprising an operation member (372, 373) which is moved by a pressure of hydraulic fluid ejected from the variable-volume pump, and which increases/decreases the ejection volume of the variable-volume pump; an elastic member which biases the operation member (372, 373) in a direction against the pressure of hydraulic fluid acting on the operation member (372, 373); the pump control unit being configured to control the variable-volume pump so that the ejection volume of the variable-volume pump equals a first ejection volume (Dmax) while the ejection pressure of the variable-volume pump is lower than a predetermined pressure, and that the ejection volume of the variable-volume pump equals a second ejection volume when the ejection pressure of the variable-volume pump reaches the predetermined pressure, the second ejection volume being smaller than the first ejection volume (Dmax), and further comprising a switch valve provided between the variable-volume pump and the operation member (372, 373), which valve is switched to a first switch position so as to block a connection to a passage communicating the variable-volume pump with the operation member (372, 373), or a second switch position so as to communicate the variable-volume pump with the operation member (372, 373), the switch valve being held in the first switch position when the ejection pressure of the variable-volume pump is lower than the predetermined pressure and switched to the second switch position when the ejection pressure of the variable-volume pump reaches the predetermined pressure characterized in that the pump control unit (14, 300, 400) includes a pressure adjustment unit provided between the variable-volume pump and the operation member (72, 73; 372, 373), which adjusts the pressure of hydraulic fluid from the variable-volume pump acting on the operation member.