An electric compressor integral with a drive circuit incorporates a compression mechanism section, a motor for driving the compression mechanism section, and a motor drive circuit. A refrigerant gas chamber having a refrigerant gas expansion space, into which refrigerant gas is introduced, is formed between a drive circuit installation section and a motor installation section, by a first partition wall provided on the drive circuit side and a second partition wall provided on the motor side, the side opposite the drive circuit side. The refrigerant gas chamber is interrupted by the first partition wall against the drive circuit installation section and is communicated with the motor installation section by a through hole that is provided in the second partition wall and through which the refrigerant gas can pass. Heat generating components, particularly in the drive circuit, can be easily and effectively cooled, and also on the motor installation side, cooling of the motor and lubrication of a bearing section can be easily and excellently performed.