A joystick includes a casing, a stick body, an identification mark and an optical sensor. The casing has a hole. The stick body is movably disposed on the casing. The stick body has a first section and a second section. The first section penetrates through the hole to protrude from the casing, and the second section is inside the casing. The identification mark is disposed on the second section of the stick body. The identification includes a first line group and a second line group crossed to each other. The first line group and the second line group respectively has a plurality of lines with different widths and arranged adjacent to each other. The optical sensor is disposed inside the casing and adapted to acquire an identification image containing the identification mark to determine a gesture of the stick body.