1. A gesture input device, comprising: an input unit to which at least one of image information and voice information representing a user's action is input; a detection unit that detects the user's action based on the input at least one of the image information and the voice information; a prediction unit that predicts one or more gestures that the user desires to input based on a detection result of the action; and a notification unit that notifies the user of an action to be performed next by the user in order to input the predicted one or more gestures.