The utility model provides a liquid level detection device installed on a thermostatic bath, the liquid level detection device comprises a liquid level detection unit, a communication unit with an inner cavity and a fixing plate, and the liquid level detection unit and the communication unit are both fixed on the fixing plate; a communicating hole is formed in a position, corresponding to the liquid level in the thermostatic bath, on the side wall of the thermostatic bath; one end of the communication unit is connected into the communication hole in a sealed mode, and an inner cavity of the communication unit is communicated with an inner cavity of the thermostatic bath. The liquid level detection device installed on the thermostatic bath can conveniently detect the liquid level height ofa medium in the thermostatic bath and send out a liquid level judgment signal, the liquid level detection device and the thermostatic bath can be kept independent of each other and complete in structure, and the liquid level detection device is convenient to install and use and can be detached at any time to be cleaned, maintained or subjected to fault detection.