To provide a monitoring system for a liquid pressure-feed device, in which operation of the liquid pressure-feed device can be detected accurately.

A float position detection switch 33, which detects the position of a float in order to detect operation of a liquid pressure-feed device, is mounted to a sealed container. A monitoring system includes: a case 36, in which the float position detection switch 33 is fixed to the sealed container; a rotary plate 38 which is mounted to be freely rotatable around a center shaft 37 of the case 36; an adhesive coil spring 39, one end of which is fixed to the rotary plate 38 and the another end of which extends above the float and which is rotated by moving up and down the float to rotate the rotary plate 38; a movable shaft 40 which is connected to the rotary plate 38 and displaced in an axis direction of the movable shaft 40 by the rotation of the rotary plate 38; a permanent magnet 41 built in the movable shaft 40; and a magnetic switch 42 which is operated by a magnetic field of the permanent magnet 41. When the float is floated up to a second predetermined height position, the magnetic switch is turned ON, and when the float is moved to a lower position than the second predetermined height position, the magnetic switch is turned OFF.