Visual inspection of interictal epileptiform discharges (IEDs) in multi-channel magnetoencephalography (MEG) requires a time-consuming evaluation process and often leads to inconsistent results among interpreters. In most clinical situations, the application of independent component analysis is restricted to artifact rejection. Here, we propose a novel extraction method for IEDs using a T/k type of blind source separation (BSST/k). We conducted comparisons of the results of BSS components with those obtained by visual inspection in sensor-space analysis for seven patients with focal epilepsy. BSST/k provided better signal decomposition of variable IEDs in one dominant component compared with sensor-space analysis. The dominant component was able to uncover IEDs that could not be detected by visual inspection, showing sufficient sensitivity along with high specificity. BSST/k was able to visualize the spreading signals over multiple channels into a single component from a single epileptogenic zone. BSST/k can be applied to focal epilepsy with a simple parameter setting. Based on the above results, we plan to develop the support analysis tool for visual identification of IEDs in future.