To provide a deterioration detector of a lubricant capable of measuring the concentration of the mixed substance of the lubricant over a wide range, and a bearing equipped with the deterioration detector of the lubricant.

The deterioration detector 1 of the lubricant is equipped with a plurality of unit deterioration detection sensors 2A-2C each of which has a floodlight projection means 3 and a light detection means 4 opposed to each other through gaps (d) where the lubricant 9 is interposed. The unit deterioration detection sensors 2A-2C are constituted so as to detect the deterioration degree of the lubricant 9 by measuring the transmitted light through the lubricant 9 between the gaps (d). The sizes of the gaps (d) of a plurality of the unit deterioration detection sensors 2A-2C are made different from each other.