PURPOSE: To record medical picture data while executing high speed compression processing with a high efficiency.

CONSTITUTION: High-order bits of picture data are compressed by a DCT circuit 31, a quantization device 32 and a variable length coder 33 and the compressed data are recorded by a recorder 16. Furthermore, the compressed data are restored by a decoder 43, an inverse quantization device 42 and an IDCT circuit 41, a difference between the original picture data and the restored data is obtained by an adder/subtractor 23 and a nonlinear converter 24 converts the difference into less bit number of data and the data are recorded through compression by a DCT/IDCT circuit 51, a quantization/inverse quantization device 52 and a variable length coding/decoding device 53.