Background: Since circulating tumor cells (CTCs) are precursors of metastatic lesions, extracting CTCs from whole blood is useful in obtaining information for cancer treatment. One of the CTC extraction methods is the size selection method; however, since the conventional methods are expensive and cumbersome, we developed an affordable and simple filter, whose usefulness is verified in this study. Methods: The new filter (hereafter, soft micropore filter [SMPF]) is made up of a polyethylene film with a thickness of 15 μm and conical pores having a diameter of 8–10 μm, which are opened uniformly (opening rate, 20%). This filter can filter whole blood by free-falling under gravity. The possibilities of the filter’s usage for model CTC extraction, immunostaining, short-term cell culture, and gene mutation detection in extracted model CTCs were verified. Results: S-MPF was able to extract model CTCs with an extraction rate of up to 15%. These model CTCs were detected by cytology, immunostaining, and culture by short-term incubation of filtered cells. Furthermore, genetic mutations were identified in the cultured cells. In addition, CTC extraction from the peripheral blood of patients with lung cancer was demonstrated by setting the volume of collected blood to 15 mL to prevent a low recovery rate. Conclusions: The S-MPF can be used to extract model CTCs quickly and easily. Moreover, cytological diagnosis, immunostaining, short-term culture, and gene mutation search are possible with this filter. Given its proven applicability in clinical samples, this sample can be used in clinical settings.