The invention relates to a sowing line position and sowing width adjusting device for a rice field seedling cultivating and sowing machine. The sowing width of the sowing machine is greater than the total width of a seedling spreading plate; the device is suspended and fixed on longitudinal beams on two sides of a rack, and is articulated with the longitudinal beams on two sides through a pair of limiting plates; the pair of limiting plates are connected with each other by virtue of a limiting rod; springs are arranged between the end part of the limiting rod and the limiting plates; the limiting plates are pressed towards the middle parts to ensure that the space M between the left limiting plate and the right limiting plate is equal to the length L of the convex middle part of the limiting rod, and M is equal to or slightly greater than the width of a seedling bed; the lower edges of the limiting plates approach to or contact the seedling bed; a bending guide part of which one end bends outwards is arranged at the front end of each limiting plate; the part, which firstly contacts the seedling bed, of the bent part of the left limiting plate or the right limiting plate swings along a hinge due to the action force of the seedling bed; the seedling bed gradually enters the part between the left limiting plate and the right limiting plate; the bending guide parts play a guide role; and when the left limiting plate and the right limiting plate depart from the center position, the spring on one side is compressed to generate restoring force.