In order to enable a still image to be checked while preventing leakage of confidential information contained in the still image, an MFP includes: an image acquiring portion to acquire a still image; an encoding portion to generate encoded data by encoding the acquired still image using an encoding key stored in advance; a decoding portion to decode the encoded data using the encoding key or a decoding key corresponding to the encoding key; and a transmitting portion to externally output the decoded still image in an electronically non-recordable form.