A lifter mechanism (16) includes: a first lifter (44) that supports an arm (24) from below and is raised and lowered between a first lower limit position and a first upper limit position; a second lifter (48) that supports the first lifter (44) from below and is raised and lowered between a second lower limit position and a second upper limit position; a first biasing member (50) that biases the second lifter (48) from the second lower limit position toward the second upper limit position; a locking lever (54) that is displaced between a locked position in which the locking lever (54) locks the second lifter (48) in the second lower limit position and a released position in which the locking lever (54) releases the lock of the second lifter (48) from the second lower limit position; a second biasing member (56) that biases the locking lever (54) from the locked position toward the released position; a holding member (58) that holds the locking lever (54) in the locked position; and a queueing lever (52) that pushes down the second lifter (48) from the second upper limit position to the second lower limit position.