A liquid mixing device that decreases a concentration non-uniformity in the flow direction of a mobile phase and a liquid chromatograph that uses the liquid mixing device are provided. The liquid mixing device is configured to include a flow channel unit that is made from an introduction channel, a branch portion that is positioned in a downstream of the introduction channel, multiple branched flow channels that branch from the branch portion, a junction portion in which the multiple branched flow channels join together, and a discharge channel of the downstream of the junction portion. The multiple branched flow channels are different in terms of any one of, or several of width, depth, and length that are associated with an external shape, and a structure filling the inside of the flow channel and thus the times for the liquid to pass through the branched flow channels are different from each other.