We demonstrate a gigapixel inline digital holographic microscopy using a consumer scanner. The consumer scanner can maximally scan an A4 size image (297mm x 210mm) with 4800 dpi (= 5.29 um), theoretically achieving a resolution of 56,144 x 39,698 = 2.22 gigapixels. The system using a consumer scanner has a simple structure, compared with synthetic aperture digital holography using a camera mounted on a two-dimensional moving stage. In this demonstration, we captured an inline hologram with 23,602 x 18,023 pixels (= 0.43 gigapixels). In addition, to accelerate the reconstruction time of the gigapixel hologram and decrease the amount of memory for the reconstruction, we applied the band-limited double-step Fresnel diffraction to the reconstruction.