An optical scanning device comprising: a micromirror device including a mirror that has a reflecting surface for reflecting light and is swingable around at least one axis, and an actuator (21, 22) that allows the mirror to swing; a control device configured to control an operation of the actuator (21, 22), wherein the control device causes the mirror to resonate with a fixed swing period by driving the actuator (21, 22); a light irradiation device configured to irradiate a back surface of the mirror on a side opposite to the reflecting surface with illumination light; a detection device to which reflected light of the illumination light that has been reflected by the mirror is incident and configured to output a position signal representing a position of the incidence light; and an abnormality detection device (7, 7A) configured to detect an abnormal operation of the mirror based on a temporal fluctuation amount of the position signal, wherein the abnormality detection device (7, 7A) includes a detection part configured to detect the fluctuation amount and a determination part (41, 41A) configured to determine whether or not the fluctuation amount is equal to or greater than a threshold value, wherein the detection part is configured of: a delay circuit that delays the position signal output from the detection device by a certain period of time, and a differential amplification circuit that amplifies and outputs a difference between the position signal output from the detection device and the position signal delayed by the delay circuit. a micromirror device including a mirror that has a reflecting surface for reflecting light and is swingable around at least one axis, and an actuator (21, 22) that allows the mirror to swing; a control device configured to control an operation of the actuator (21, 22), wherein the control device causes the mirror to resonate with a fixed swing period by driving the actuator (21, 22); a light irradiation device configured to irradiate a back surface of the mirror on a side opposite to the reflecting surface with illumination light; a detection device to which reflected light of the illumination light that has been reflected by the mirror is incident and configured to output a position signal representing a position of the incidence light; and an abnormality detection device (7, 7A) configured to detect an abnormal operation of the mirror based on a temporal fluctuation amount of the position signal, wherein the abnormality detection device (7, 7A) includes a detection part configured to detect the fluctuation amount and a determination part (41, 41A) configured to determine whether or not the fluctuation amount is equal to or greater than a threshold value, wherein the detection part is configured of: a delay circuit that delays the position signal output from the detection device by a certain period of time, and a differential amplification circuit that amplifies and outputs a difference between the position signal output from the detection device and the position signal delayed by the delay circuit. a delay circuit that delays the position signal output from the detection device by a certain period of time, and a differential amplification circuit that amplifies and outputs a difference between the position signal output from the detection device and the position signal delayed by the delay circuit.