A video encoding/decoding apparatus including a video encoder for generating a prediction block, generating a residual block by subtracting the prediction block from the current block. The video encoder is for generating a frequency-transformed block by transforming and quantizing the residual block, generating a masked frequency-transformed block by masking the frequency-transformed block by using one or more frequency mask tables. The video encoder is for encoding information about a frequency mask table used for masking the masked frequency-transformed block. The apparatus includes a video decoder for extracting a masked quantized frequency coefficient string recorded in the bitstream. The video decoder is for generating a quantized frequency coefficient string by zero setting all quantized frequency coefficients at positions of no records in the bitstream from a masked quantized frequency coefficient string. The video decoder is for generating a quantized frequency-transformed block by inversely scanning the generated quantized frequency coefficient string.