Provided is a sample pretreatment device configured to apply, to the surface of a sample, a solution in which a predetermined substance is dissolved or dispersed. In order to properly and efficiently unclog a nozzle due to the deposition of the crystal of a matrix substance, the device includes a spray unit (3) including a solution tube (32) for the solution to pass through, a gas tube (33) for a spray gas to pass through, and a nozzle part (30) configured to spray the solution arriving at the terminal end of the solution tube by ejection of the spray gas through the gas tube, as well as a cleaning liquid supplier (4, 41) configured to put a cleaning liquid on an opening of the nozzle part from outside the spray unit.