An image forming apparatus includes a printing head having an ink nozzle configured to discharge ink droplets onto a recording medium in order to form an image on the recording medium in a recording operation; a carriage on which the printing head is mounted and being moved in a main-scan direction during the recording operation; a linear encoder sheet having a counter for detecting a position of the carriage; an encoder sensor mounted on the carriage and detecting the position of the carriage by optically reading the counter of the linear encoder sheet; an carriage unit enclosure in which at least the carriage, the linear encoder sheet, and the encoder sensor are disposed; and an internal pressure adjusting unit adjusting an internal pressure of the carriage unit enclosure to be other than a negative pressure.