A washing bath in a photographic paper processor has plural washing chambers for washing photographic paper with washing water by passage of the photographic paper. Plural cell units are coupled with one another vertically by a modular structure. Each of the cell units has one of the washing chambers. A sealing medium of silicone rubber keeps a cell connection portion between the cell units in a liquid-tight state. A blade mechanism is secured to a panel constituting the cell units, allows the photographic paper to pass between the washing chambers, and blocks passage of the washing water. A transporting rack transports the photographic paper serially to pass the washing chambers. The cell connection portion includes a connection surface, disposed to extend horizontally, and separable for removal of the cell units in the vertical direction. The sealing medium is secured to one of two cell units being coupled.