Disclosed is a compact rotary cylinder device wherein rotating parts which are capable of rotating at a uniform speed around a shaft are compactly mounted in both the axial direction and the radial direction of the device, and the rotary motion of the rotating parts around a plurality of crank shafts is combined so as to enable the linear reciprocating motion of a piston group, and noise reduction is achieved by suppressing rotation-induced vibrations by achieving mass balance of the rotating parts. First, second and third rotational balances are balanced by means of first and second balance weights (9, 10). The first rotational balance is of first and second piston groups (7, 8), centred around second virtual crank shafts (14a, 14b); the second rotational balance is of a piston complex (P), centred around a first crank shaft (5); and the third rotational balance is of the first crank shaft (5) and the piston complex (P), centred around a shaft (4). Whilst in the described balanced state, the first crank shaft (5) rotates around the shaft (4), and the piston complex (P) rotates around the first crank shaft (5), thus the first and second piston groups (7, 8) which are mounted in a second cylinder (6b) move in a linear reciprocating manner along the radial direction of the rolling circle (23) of the second virtual crank shafts (14a, 14b), the rolling circle being centred on the shaft (4) and having a radius of 2r.