Rotary electric shaver and method of manufacturing inner blade of rotary electric shaver

A rotary electric shaver comprising:

• wherein the rotary electric shaver is in an upright position;
• an outer blade whose upper surface functions as annular shaving surfaces having multiple hair inlets formed therein;
• and
• an inner blade operatively positioned within the outer blade for rotation and being in slidable contact with a lower surface of the outer blade from below the annular shaving surfaces,
• wherein the inner blade, including a centrally formed recessed portion, a projection and a concave portion, is an integral structure using a metal material, and includes an inner blade base plate having the centrally formed recessed portion extending downwardly from the inner blade base plate with the projection extending upwardly from a center position of the recessed portion, said projection including an upper surface side defining a convex portion and a lower surface side defining the concave portion at the center position in a radial direction,
• wherein an upper end portion of an inner blade drive shaft directly engages with the concave portion so as to be disengageable therefrom,
• wherein the projection extends upwardly from a position located under a plate surface of an inner blade base plate by forming the recessed portion around the projection,
• wherein a shape of the concave portion is polygonal shaped,
• wherein a through-hole is formed at a radial center of the concave portion,
• wherein a side portion of the concave portion has a curvature in an axial direction, and
• wherein an upper end portion of the drive shaft has a shape corresponding to the shape of the concave portion and engages with the concave portion.