Steering Device

A fastening mechanism fastens a first side plate to a second side plate by a fastening member. A boss with a rhombic cross-section of the fastening member is inserted into a telescopic-adjust long groove of the second side plate. An outer periphery of the boss includes a first corner part and a third corner part each forming an obtuse angle and facing each other. The first corner part is disposed on an upper side in an axial direction, on a lower side in a tilt direction, while the third corner part is disposed on a lower side in the axial direction, on an upper side in the tilt direction. A width across the first corner part and the third corner part is shorter than a groove width W of the telescopic-adjust long groove.