An input video signal is coded by a 1-pass type coding system highly efficiently by taking the proportions of the components of the input image. The coding difficulty level computation circuit 33 determines the coding difficulty level d of the input moving image signal S1 and sends it to the amount of allocated bits computation circuit/controller 34. The amount of allocated bits computation circuit/controller 34 determines a reference value of amount of allocated coding bits on the basis of the coding difficulty level d and, when shifting the reference value to the actual amount of allocated coding bits b_x, it stores part of the sum of the amounts of allocated bits a per unit time for a certain period of time as virtual buffer in advance and the actual reference value of the amount of allocated coding bits is obtained by dividing the sum of the amounts of allocated coding bits per unit time less the part stored as virtual buffer by said period of time. As long as the virtual buffer is positive, the provision of an amount of bits exceeding said reference value is permitted.