An apparatus for measuring ocular and/or blood glucose levels comprises (a) an irradiating means (10) for irradiating light onto the eye (1) of a user from outside the cornea of the eye to excite an ocular glucose sensor in contact with an ocular fluid, said sensor being able to emit a total fluorescence having first and a second wavelength bands; (b) an optical path splitting means (11) for splitting said total fluorescence into a first fluorescence and a second fluorescence, said first fluorescence and said second fluorescence traveling along first and second optical paths; (c) a first detecting means (14) located in the first optical path; (d) a second detecting means (17) located in the second optical path; (e) a calculating means for calculating the intensity ratio of the first fluorescence to the second fluorescence and for determining an ocular glucose concentration in the ocular fluid; and (f) an arithmetic means for converting the ocular glucose concentration into a blood glucose concentration.