a subassembly including

a holder including a mounting portion, an engaging section, and a projection,

a laser diode array disposed on the mounting portion of the holder and having at least three light emitting points arranged in a package at an equal interval and configured to emit respective laser beams that form corresponding laser beam spots on a recording medium at a minimum recording interval, and

a collimator lens disposed on the projection;

a bracket defining an engaging hole, the engaging hole of the bracket surrounding and contacting the engaging section of the holder;

an abnormal lighting detector configured to detect abnormal lighting of the one of the at least three light emitting points configured to emit a clock laser beam; and

a laser beam changer configured to change the clock laser beam to any one of the laser beams emitted by the other light emitting points normally emitting a laser beam, when the abnormal lighting detector detects abnormal lighting,

wherein

the holder and the bracket define voids configured to permit rotation of the holder relative to the bracket before securing the holder to the bracket, and the laser beams from the at least three light emitting points scan the recording medium in a main scanning direction while being at least one of on and off so as to form a light image having the minimum recording interval in the recording medium,

the equal interval is smaller than the minimum recording interval,

the at least three light emitting points are arranged such that the corresponding laser beams spots on the recording medium are arranged substantially in a line in a direction orthogonal to the main scanning direction, and

any one of the laser beams is used as the clock laser beam configured to determine a timing of starting each main scanning.