A concrete vibrator powered by a portable drill includes a housing having a contacting pad at one end and an axial bore. A camshaft is received within the bore. A transverse retainer is secured on the camshaft for retaining the camshaft within the bore. The camshaft includes a pair of cam surfaces at one end. A cam follower is disposed within the bore for engaging the cam surfaces when the camshaft is rotated. The cam follower and cam surfaces cooperatively cause axial reciprocation of the rotating camshaft for producing axial vibration of the housing face. The axial bore includes a radially expanded portion to receive the retainer and prevent complete withdrawal of the camshaft. The camshaft includes a transverse bore for receiving the retainer within the radially expanded portion. The retainer has a spring bearing against a trapped ball projecting beyond the cylindrical surface of the camshaft.