The request on miniaturization of optical pickup has invoked the development of several new architectures and relevant optical components. The optical pickup mostly composed of reflective optical components tends to have the smallest form factor due to the forward and backward light path being folded and restricted within a common space. The optical component for the quadratic detector to generate focal error signal (FES) should also be reflective type and has to work in off-axis fashion. The parameters which influence the performance of the off-axis astigmatic reflector at finite conjugate has been investigated and a systematic design procedure based on optimizing an off-axis portion of a biconic surface has been developed. The design example shows normalized FES curve with sufficient linearity and sensitivity for the detection of disc deviation within the range of ±1 mm for the pickup working at 405 nm.