A connection device for connecting to a connection arm comprising: a first connection portion in which a first guide space is formed, the connection arm being inserted in the first space; a second connection portion provided below the first connection portion, a second guide space being formed in the second connection portion, the connection arm being inserted in the second space; a first rod guide portion provided above the first guide space, and a first hole being formed in the first rod guide portion; a second rod guide portion provided above the second guide space, and a second hole being formed in the second rod guide portion; a first arm receiving portion being pushed by the connection arm to rotate from a standby state when the connection arm is inserted into the first guide space; a second arm receiving portion being pushed by the connection arm to rotate from a standby state when the connection arm is inserted into the second guide space; a link member configured to connect the first arm receiving portion and the second arm receiving portion such that the first arm receiving portion and the second arm receiving portion rotate in conjunction with each other; and a connection rod passed through the first hole and the second hole; characterized in that each of the first and second arm receiving portions is provided with a passed-through portion; the passed-through portion is formed such that when the each of the first and second arm receiving portions has been rotated upward, the connection rod can be passed in the vertical direction; the passed-through portion is formed in the middle and upper regions of the each of the first and second arm receiving portions; the first arm receiving portion has a wall forming the lower end of the passed-through portion; and the wall forms a rod retaining portion; and the rod retaining portion is configured to support a lower end of the connection rod within the first guide space when the first arm receiving portion is in the standby state, and the rod retaining portion configured to rotate together with the first arm receiving portion to allow the connection rod to pass through the second hole so that the connection rod is allowed to be connected to the connection arm inserted into the first guide space or the second guide space, when the first arm receiving portion rotates from the standby state. a first connection portion in which a first guide space is formed, the connection arm being inserted in the first space; a second connection portion provided below the first connection portion, a second guide space being formed in the second connection portion, the connection arm being inserted in the second space; a first rod guide portion provided above the first guide space, and a first hole being formed in the first rod guide portion; a second rod guide portion provided above the second guide space, and a second hole being formed in the second rod guide portion; a first arm receiving portion being pushed by the connection arm to rotate from a standby state when the connection arm is inserted into the first guide space; a second arm receiving portion being pushed by the connection arm to rotate from a standby state when the connection arm is inserted into the second guide space; a link member configured to connect the first arm receiving portion and the second arm receiving portion such that the first arm receiving portion and the second arm receiving portion rotate in conjunction with each other; and a connection rod passed through the first hole and the second hole; characterized in that each of the first and second arm receiving portions is provided with a passed-through portion; the passed-through portion is formed such that when the each of the first and second arm receiving portions has been rotated upward, the connection rod can be passed in the vertical direction; the passed-through portion is formed in the middle and upper regions of the each of the first and second arm receiving portions; the first arm receiving portion has a wall forming the lower end of the passed-through portion; and the wall forms a rod retaining portion; and the rod retaining portion is configured to support a lower end of the connection rod within the first guide space when the first arm receiving portion is in the standby state, and the rod retaining portion configured to rotate together with the first arm receiving portion to allow the connection rod to pass through the second hole so that the connection rod is allowed to be connected to the connection arm inserted into the first guide space or the second guide space, when the first arm receiving portion rotates from the standby state.