1. Intoroduction Recently, various time-of-flight (TOF) range imagers [1-4] have been developed, and are becoming popular in 3D acquisition cameras. This is because TOF range imagers have a high-speed capturing capability, and their millimetric range resolutions are sufficient for their applications such as gesture recognition. However, to apply the TOF range imagers to contactless 3D scanners, further higher range resolution is strongly desired. This paper presents a TOF range imager with 140 um range resolution of a single frame, which corresponds to sub-picosecond time resolution. The developed TOF range imager employs a three-tap lock-in pixel with draining structure, which allows us to enhance a utilization efficiency for a received light. A self-calibration technique [5] for a clock skew of column-parallel gating clocks is introduced to the TOF measurement with the 3-tap lock-in pixel, which shorten calibration time to be several tens of μs.