We developed a high-speed linear detection time-domain optical coherence tomography (OCT) technique that detected a reflective grating-generated spatial optical delay in the reference arm using a line scan camera during probe-beam scanning. Using an InGaAs line scan camera (512 pixels) operating at $47,000\text{\hspace{0.17em} lines}/\mathrm{s}$ , the calculation of the absolute value of the difference between two sequential lines can be approximately displayed as cross-sectional images with 500 lateral pixels at $94\text{\hspace{0.17em} frames}/\mathrm{s}$ . After data acquisition, we performed postprocessing that involves a Hilbert transform to improve the image quality of an OCT image. Our OCT system was successfully used to image a human finger in vivo with $93\mathrm{dB}$ sensitivity.