To provide a new carbazole derivative providing a guest material in a light-emitting layer giving blue to blue green color phosphorescence of an organic EL element capable of emitting triplet light, and a polymer-based host material having a minimum excitation triplet energy and being used by its application, also capable of making a film by applying, and useful as a photo-converting element, an electrophotography, a thermochromic element, an optical memory element, etc.

This carbazole derivative is expressed by general formula (1) in image 1 (wherein, R, R1 to R8, R1' to R8' may be the same or different and are each H or a substituting group; and X is a single bond or a divalent organic group).