The paper deals with some major themes in early Cassirer's philosophy of mathematics. It appears, that the basis of his thinking about mathematical objects and mathematical concept formation is his Neo-Kantian idealistic (transcendental) theory of concepts which he developed in opposition to what is called the 'traditional theory of concepts' going back to Aristotle. Cassirer often seeks to confirm his philosophical insights concerning mathematics by the interpretations the works of significant mathematicians. Therefore, the second part of the paper deals with Cassirer's attempt to find such a confirmation in famous Dedekind's theory of natural numbers. Cassirer's philosophical attitude to Dedekind's theory is compared with that of Russell. The author raises the sceptical question of whether Cassirer's view of mathematics - as developed in his early period - could be a sufficient or at least plausible basis for solving philosophical problems of the foundations of mathematics of that time.