We present SQUIDPOL, a low-cost, multi-channel optical imaging polarimeter that performs simultaneous linear polarization measurements using a rotating half-wave plate, a non-polarizing beam splitter, and four wire-grid filters. We show that the multilayer dielectric coating of the off-the-shelf non-polarizing beam splitter introduces different phase delays to the s- and p-polarized components, which introduces polarization-dependent systematics that can bias polarimetric measurements if left uncorrected. We quantify this effect for both transmitted and reflected beams and incorporate a correction scheme into the data-analysis pipeline. On-sky validation demonstrates stable and reproducible performance, achieving a polarization accuracy of σP ∼ 0.15% for bright polarimetric standard stars (V ∼ 2–3 mag). Mounted on the 60-cm Ritchey-Chrétien telescope (focal length of 4200 mm, f/7) at the Pyeonchang Observatory of Seoul National University, SQUIDPOL provides an effective common field of view of 13.5′ × 8.2′ with a pixel scale of 0.45′′ pixel−1 and supports standard B, V , RC, and IC filters.