To provide a mouse device that can secure stable operation by removing influence of a surface state of an operation surface to the utmost and can be used even on the lower surface of a vertical surface and a horizontal surface.

The mouse device is provided with a position detecting means 12 to detect a transfer position of a mouse main body 11 and a mouse ball 13 to transmit the transfer direction and transfer quantity of the mouse main body 11 to the position detecting means 12 by being synchronously rolled with transfer of the mouse main body 11, the plural mouse balls 13 are provided at the bottom of the mouse main body 11 at specified distance in its surface direction, and a part of each mouse ball 13 is held in a state that it is always projected from the bottom surface of the mouse main body 11.