Record‐breaking heavy rainfalls in 2003 and 2006 induced major aggradation along Paradai and Rubeshubenai Creeks, mountain streams in Saru River system, Hokkaido. This study addresses the channel response following aggradation along 1750‐m and 2250‐m study reaches of Paradai and Rubeshubenai Creeks, respectively. Twenty years of cross‐sectional survey data documented spatial variability in the channel response along the study reaches. In the upper reach, erosion of aggraded sediment began in the following year and stopped three years (Paradai) to five years(Rubeshubenai) later. On the other hand, in the middle reach, no major progress in erosion had been made because of sediment inflow while the erosion in the upper reach continued, and after that, the erosion increased, and then it stopped later than the upper reach. Processes of channel recovery after aggradation varied according to the magnitude of morphological change imposed in a cross section. When the change is minor, for example aggradation only within a bankfull channel or aggradation across a narrow (around10m in width) valley floor, newly aggraded sediment thoroughly eroded in two or three years, so that the channel recovered to its former profile. When the change is major, i.e., when a wide (around 20m and more in width) valley floor is entirely buried by sediment and turns into a wide, flat channel bed, initiation and incision of a new channel began. Channel cross section enlarged, and channel bed surface coarsened over time. Five to seven years later the channel stopped its evolution. This shows that the channel has attained an equilibrium state. The equilibrium channel was characterized by bed surface coarsening in both study sites. The degree of that coarsening was that d100―d95 particle size of surface sediment corresponded to particle size for critical shear stress at annual maximum discharges during the period of channel evolution.