An image generation system performs a game process of causing a game character to make a predetermined movement for a given object based on an operation input from an operation section including an acceleration sensor and causing the given object to move in an object space. The image generation system includes: an operation input detection section which detects whether or not a plurality of operation inputs including a first operation input and a second operation input for causing the game character to make a predetermined movement have been performed based on an output value from the acceleration sensor; a character movement control section which controls the game character to make a predetermined movement based on the first operation input; and an object movement control section which controls a movement state of the given object based on at least one of the first operation input and the second operation input.