We have searched for pulsation of the anomalous X-ray pulsar (AXP) 4U 0142+61 in the K' band (lambda(eff) = 2.11 mu m) using the fast-readout mode of Infrared Camera and Spectrograph (IRCS) at the Subaru 8.2 m telescope. We found no significant signal at the pulse frequency expected by the precise ephemeris based on an X-ray monitoring observation with RXTE. Nonetheless, we obtained the best upper limit of 17% (90% C.L.) for the root-means-quare pulse fraction in the K' band. Combined with the i' band pulsation (Dhillon et a]. 2005, MNRAS, 363, 609), the slope of the pulsed component (F-nu alpha nu(alpha) in units of Jy) was constrained to alpha > -0.87 (90% C.L.) for an interstellar extinction of A(V) = 3.5.