A driving assistance system (1, 1B, 1C) to provide various kinds of information to a driver of a moving object from an image-capturing result of surroundings of the moving object, comprising: image-capturing means installed on the moving object and configured to capture a surrounding image including a portion of the moving object; first edge line storing means (22,25) configured to store a first edge line detected for the portion of the moving object from a first surrounding image captured in advance by the image-capturing means in normal conditions when no raindrops are attached to a lens unit of the image capturing means; edge detecting means configured to detect a second edge line for the portion of the moving object from a second surrounding image currently captured by the image-capturing means; calculating means configured to calculate a deviation degree between the first edge line stored in the first edge line storing means (22,25) and the second edge line detected by the edge detecting unit; raindrop judging means configured to judge that a raindrop is attached to the lens unit of the image-capturing means, when the deviation degree between the first edge line and the second edge line is equal to or larger than a predetermined value, and detection sensitivity lowering means configured to lower sensitivity of detection of another moving object from the second surrounding image currently captured by the image-capturing means by raising a detection threshold to detect another moving object from the second surrounding image, when the raindrop judging means judges that a raindrop is attached to the lens unit of the image-capturing means and the deviation degree between the first edge line and the second edge line is lower than a preset given value which is a value larger than the predetermined value. image-capturing means installed on the moving object and configured to capture a surrounding image including a portion of the moving object; first edge line storing means (22,25) configured to store a first edge line detected for the portion of the moving object from a first surrounding image captured in advance by the image-capturing means in normal conditions when no raindrops are attached to a lens unit of the image capturing means; edge detecting means configured to detect a second edge line for the portion of the moving object from a second surrounding image currently captured by the image-capturing means; calculating means configured to calculate a deviation degree between the first edge line stored in the first edge line storing means (22,25) and the second edge line detected by the edge detecting unit; raindrop judging means configured to judge that a raindrop is attached to the lens unit of the image-capturing means, when the deviation degree between the first edge line and the second edge line is equal to or larger than a predetermined value, and detection sensitivity lowering means configured to lower sensitivity of detection of another moving object from the second surrounding image currently captured by the image-capturing means by raising a detection threshold to detect another moving object from the second surrounding image, when the raindrop judging means judges that a raindrop is attached to the lens unit of the image-capturing means and the deviation degree between the first edge line and the second edge line is lower than a preset given value which is a value larger than the predetermined value.