To provide connection structure between an electromagnetic clutch type brake device and a rotary shaft such as a motor rotary shaft, which can avoid the generation of backlash without applying adhesives.

The outer peripheral irregular structure 12 formed around a motor shaft 11 is formed integral with a metal rotary shaft 11 into a gear shape. The inner peripheral irregular structure 20 formed on an input side rotary shaft 31 is formed integral with the input side rotary shaft 31 made of deformable elastic resin material into a gear shape so that the tip of each projected section 21 is branched into two section in the peripheral direction. Since the projected section 21 whose tip is branched into two section is made of elastic material, it has flexibility, and the width of the tip is variable in the peripheral direction. That is, in a natural state in which pressure is not applied to the tip of the projected section 21, the width of the tip of the projected section 21 in the peripheral direction is set so as to be larger than that of the peripheral direction of the recessed section of the outer peripheral irregular structure 12, which is to be meshed with the section 21. While they are connected to each other, the two tips of branched projected section are press-fitted in the recessed section of the outer peripheral irregular structure 12 while the two tips of the branched projected section 21 is deformed in the inside direction.