A current mirror device includes an input end for receiving an input signal, an output end for outputting an amplified signal of the input signal, first through third transistors, and an operational amplifier. The first transistor includes a first end coupled to first reference current and a second end coupled to a bias voltage. The control end of the second transistor is coupled to the input end. The third transistor includes a first end coupled to the output end, a second end coupled to the first end of the second transistor and a control end coupled to a reference voltage. The operational amplifier is configured to keep a first voltage and a second voltage at substantially the same level, wherein the first voltage is obtained on the first end of the first transistor and the second voltage is obtained on the first end of the second transistor. Therefore, the reference current flowing through the first transistor can be accurately amplified to a desired value and mirrored to become load current flowing through the second transistor.