A rotary electric shaver comprising: a main body having a drive shaft and a connection part ; a first head having a plurality of first blade units having a first outer blade , a first inner blade rotating while coming into sliding contact with an inner surface of the first outer blade , and a first driven shaft that rotates the first inner blade , having a built-in first transmission drive system connected to the drive shaft to rotate the first driven shaft , and detachably connected to the connection part ; the rotary shaver being characterized by : a second head detachably connected to the connection part from which the first head is removed, wherein the second head has a plurality of second blade units having a second outer blade and a second inner blade reciprocating while coming into sliding contact with an inner surface of the second outer blade , and having a built-in second transmission drive system connected to the drive shaft to cause the second inner blade to reciprocate, and wherein the second transmission drive system has an eccentric shaft and a plurality of oscillators that convert a rotational motion of the eccentric shaft into a reciprocating motion, and rotates the eccentric shaft at a rotation speed higher than a rotation speed of the first driven shaft . a main body having a drive shaft and a connection part ; a first head having a plurality of first blade units having a first outer blade , a first inner blade rotating while coming into sliding contact with an inner surface of the first outer blade , and a first driven shaft that rotates the first inner blade , having a built-in first transmission drive system connected to the drive shaft to rotate the first driven shaft , and detachably connected to the connection part ; the rotary shaver being characterized by : a second head detachably connected to the connection part from which the first head is removed, wherein the second head has a plurality of second blade units having a second outer blade and a second inner blade reciprocating while coming into sliding contact with an inner surface of the second outer blade , and having a built-in second transmission drive system connected to the drive shaft to cause the second inner blade to reciprocate, and wherein the second transmission drive system has an eccentric shaft and a plurality of oscillators that convert a rotational motion of the eccentric shaft into a reciprocating motion, and rotates the eccentric shaft at a rotation speed higher than a rotation speed of the first driven shaft . a second head detachably connected to the connection part from which the first head is removed, wherein the second head has a plurality of second blade units having a second outer blade and a second inner blade reciprocating while coming into sliding contact with an inner surface of the second outer blade , and having a built-in second transmission drive system connected to the drive shaft to cause the second inner blade to reciprocate, and wherein the second transmission drive system has an eccentric shaft and a plurality of oscillators that convert a rotational motion of the eccentric shaft into a reciprocating motion, and rotates the eccentric shaft at a rotation speed higher than a rotation speed of the first driven shaft . <EOS>