This paper describes the navigation and the guidance strategy of the small spacecraft for flyby using the images of the target. We derived navigation and guidance accuracies of this mission analytically, and confirmed them by numerical simulation. For high accurate flyby, the center of the target needs to be measured accurately. However the shade area on the target surface makes it difficult to know the target center position from the information of the center of brightness in image. This uncertainty affects the guidance accuracy from the target. In this paper, a method to calculate the target center from the tangent points of the sun is proposed. The validity of the method is examined in the experiment.