A wet processing apparatus for wet-processing substrates can suppress the reduction of throughput when some component part thereof becomes unserviceable. The wet processing apparatus includes a first nozzle unit and a second nozzle unit. When the wet processing apparatus operates in a normal mode, a substrate carrying mechanism is controlled so as to deliver substrates alternately to processing units of a first group and those of a second group so that the substrates are processed sequentially in order. When the processing units of the first group (the second group) are unserviceable due to the inoperativeness of the substrate holders, a processing liquid supply system or a nozzle support mechanism, the nozzle unit for the processing units of the second group (the first group) is moved to process substrates by the serviceable ones of the first group (the second group).