A liquid state detecting sensor for detecting a state of a liquid including a liquid concentration detecting element, a holder member, and an enclosing member as defined herein, wherein the holder member has a configuration in which respective portions of a lower end surface facing the enclosed region are located higher than or at a same height as a lowest hole periphery at the rim of the element holding hole from which the detecting element protrudes, and at least one of circulation holes formed in the enclosing member is a bubble-discharging hole which has an upper end located higher than the lowest hole periphery and a lower end located lower than a surface peripheral edge of the lower end surface.