Paper feeding device and image forming apparatus

A paper feeding device, comprising:

• a storing section which is removably fitted to a device main body, and in which a recording medium is stored;
• a transport section which feeds out and transports, sheet by sheet, the recording medium stored in the storing section;
• a lifting section which is provided in the storing section and on which the recording medium is placed, and which is raised and lowered between a retreat position closest to the bottom face of the storing section and a paper-feeding position at which the topmost face of the placed recording medium abuts the transport section;
• a driving section which raises and lowers the lifting section;
• a measurement unit which is disposed above the lifting section and which measures a distance down to the topmost face of the recording medium placed on the lifting section when the lifting section is at the retreat position;
• a sheet number calculation unit which calculates the number of sheets of the recording medium that is placed on the lifting section, on the basis of the distance to the topmost face of the recording medium as measured by the measurement unit;
• and
• a power control unit which has an ordinary mode in which power is supplied to the transport section, the driving section, the measurement unit and the sheet number calculation unit, and a power saving mode in which power is supplied to the measurement unit and the sheet number calculation unit, and which controls a supply of power to the sections and units, wherein
• in the ordinary mode, the driving section displaces the lifting section in such a manner that the lifting section is at the paper-feeding position at all times, and in the power saving mode, the driving section displaces the lifting section in the retreat position.