A time-synchronization technique for secure visible light communication and positioning is proposed. A transmit signal composed of multiple sinusoidal carriers from an LED light illuminates a reflector. By using phases of the carriers obtained from a single captured image with a rolling-shutter camera, the proposed technique estimates the time difference between the start time of the transmitted signal and the shutter release time of the camera. The experimental results confirmed that the technique could achieve mean absolute errors of 4.663 \(\times \) 10 \(^{-6}\) [s], root mean square errors of 6.398 \(\times \) 10 \(^{-6}\) [s] and 90th percentile errors of 1.008 \(\times \) 10 \(^{-5}\) [s], respectively, which were higher time resolutions than those achievable using a rolling-shutter camera with a given frame rate and a number of its line sensors.