An image forming apparatus that is capable of communicating with an external device via a network and operates by switching between a first power state and a power saving state in which electric power consumption is lower than in the first power state, the image forming apparatus characterized by: a human sensor configured to detect whether a person is present or absent within a predetermined area; an image forming section configured to form an image on a recording medium; an internal sensor configured to detect a state of the image forming section; a power supply section configured to supply electric power to the internal sensor; a controller configured to control the image forming section and the power supply section; and a communication section configured to communicate with the external device, wherein the internal sensor includes: a first internal sensor configured to detect a quantity that varies by operation of the image forming section; and a second internal sensor configured to detect a state of operation of the image forming section; the communication section is configured to communicate a result detected by the first internal sensor to the external device, and in the power saving state, the controller controls, based on a result of detection of a change between presence and absence of the person within the predetermined area performed by the human sensor, the power supply section to supply electric power to the first internal sensor to cause the first internal sensor to detect the quantity that varies by the operation of the image forming section, and not to supply electric power to the second internal sensor. a human sensor configured to detect whether a person is present or absent within a predetermined area; an image forming section configured to form an image on a recording medium; an internal sensor configured to detect a state of the image forming section; a power supply section configured to supply electric power to the internal sensor; a controller configured to control the image forming section and the power supply section; and a communication section configured to communicate with the external device, wherein the internal sensor includes: a first internal sensor configured to detect a quantity that varies by operation of the image forming section; and a second internal sensor configured to detect a state of operation of the image forming section; a first internal sensor configured to detect a quantity that varies by operation of the image forming section; and a second internal sensor configured to detect a state of operation of the image forming section; the communication section is configured to communicate a result detected by the first internal sensor to the external device, and in the power saving state, the controller controls, based on a result of detection of a change between presence and absence of the person within the predetermined area performed by the human sensor, the power supply section to supply electric power to the first internal sensor to cause the first internal sensor to detect the quantity that varies by the operation of the image forming section, and not to supply electric power to the second internal sensor.