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 (31a, 31b) 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 (31a, 31b) 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 (31a, 31b) 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.