A video game apparatus as a sound output apparatus includes a CPU, and the CPU detects acceleration data included in input information data transmitted from a controller. The acceleration data is numerical value data for accelerations in three axial directions set to the controller. For example, a swinging motion of the controller in a right direction or a left direction is determined based on the acceleration in a direction of one axis (x-axis) out of three axes. In addition, a downward swinging motion of the controller and a posture of the controller at the time of end of swing are determined based on the acceleration in directions of two axes (y-axis and z-axis) other than the one axis. Accordingly, for example, a performance of a musical instrument displayed on a game screen is individually instructed.