The invention relates to a device for keeping to one side. The device comprises a support, a rotating shaft, an edge distance switching wheel, a first switching position top block, a second switching position top block and a locating piece for keeping to one side. The rotating shaft is supported on the support and simultaneously has rotational freedom and sliding freedom relative to the support. The locating piece for keeping to one side sleeves the rear end of the rotating shaft. The edge distance switching wheel is in fastened connection with the front end of the rotating shaft, and the rotating shaft between the edge distance switching wheel and the support is sleeved with a spring. The edge distance switching wheel is provided with a first locating groove and a second locating groove, wherein openings of both the first locating groove and the second locating groove are forwards. The front end of the support is connected with the first switching position top block and the second switching position top block. The distance between the first switching position top block and the front end of the support and the distance between the second switching position top block and the front end of the support are unequal. The edge distance switching wheel has two working states. When the edge distance switching wheel is in a first working state, the first locating groove is in close fit with the first switching position top block; and when the edge distance switching wheel is in a second working state, the second locating groove is in close fit with the second switching position top block.