The invention concerns a combined piston-expander compressor comprising a plurality of pistons (3, 14) which are mechanically coupled together by a piston rod (4), as well as a main slide (6), an auxiliary slide (7) and a control valve (9) for control purposes, characterized in that the main slide (6) is formed from a plurality of slide elements that are not interconnected, two outer slide bodies (6a, 6b) being provided. Control pistons (6c) with control edges and simple slide elements (6d) are arranged in a row between the outer slide elements, in the form of a small piston (6a) and a large piston (6b), such that a differential pressure acting on the outer slide elements (6a, 6b) automatically and mechanically holds together the main slide (6).