Flagstadelva is a river in Innlandet county, Norway. The 32.6-kilometre (20.3 mi) river begins in the Lavsjømyrene bog areas in northern Løten Municipality. From there it runs in a southerly direction and forms the lake Nybusjøen. The river flows through Hamar Municipality and for a short distance forms the border with Ringsaker Municipality too. The river runs through a v-shaped valley which twists before its mouth at the town of Hamar where it empties into the lake Mjøsa. The river's erosion has exposed the lower Cambrian and middle Cambrian rock formations in that region.