A probe array substrate suitable for forming a probe array that has high packing density, that can hold sufficient amounts of probe molecules, and that has little variation in the amounts of probe molecules. A plurality of arrayed probe-holding portions are defined by recesses, and isolating grooves are formed between the adjacent probe-holding portions to prevent probe solutions introduced into the probe-holding portions from spreading to adjacent probe-holding portions. Inner surfaces of the probe-holding portions are made hydrophilic, whereas inner surfaces of the isolating grooves are made hydrophobic. Liquid-introducing protrusions are formed in the probe-holding portions.