An object detector comprising: an optical scanner including: a light source unit configured to emit a light beam; and a light deflector configured to deflect the light beam emitted from the light source unit to scan an object in a detection region with the deflected light beam, a light receiving optical element configured to collect the light beam returned from the object through at least one of reflection or scatter on the object in the detection region in response to scanning with the light beam deflected by the light deflector; and a light receiving element configured to receive the light beam collected by the light receiving optical element, the light receiving element including multiple light receiving pixels arranged in a first direction at different positions on a plane perpendicular to the optical axis; wherein the multiple light receiving pixels are further arranged in a second direction intersecting the first direction to form a pixel array; characterized in that the light deflector satisfies the mathematical expressions below: 2 tan − 1 d 2 f r < θ t ≤ 2 tan − 1 Nd + N − 1 p 2 f r − 8 A sin L c ω s when N is an even number equal to 2m where m is a natural number; and 2 tan − 1 d + 2 p 2 f r < θ t ≤ 2 tan − 1 Nd + N − 1 p 2 f r − 8 A L c ω s when N is an odd number equal to 2m + 1 where m is a natural number where ω s is a sinusoidal angular velocity of scanning, A is a maximum mechanical deflection angle, L is a maximum detection distance, f r is a focal length of the light receiving optical element, d is a width of each of the light receiving pixels in the first direction, p is a distance in the first direction between adjacent light receiving pixels, c is the speed of light, θ t is a spread angle of projecting light, and N is the number of pixel arrays arranged along a direction in which horizontal shift occurs in the light receiving element due to an angle change of the light deflector. an optical scanner including: a light source unit configured to emit a light beam; and a light deflector configured to deflect the light beam emitted from the light source unit to scan an object in a detection region with the deflected light beam, a light source unit configured to emit a light beam; and a light deflector configured to deflect the light beam emitted from the light source unit to scan an object in a detection region with the deflected light beam, a light receiving optical element configured to collect the light beam returned from the object through at least one of reflection or scatter on the object in the detection region in response to scanning with the light beam deflected by the light deflector; and a light receiving element configured to receive the light beam collected by the light receiving optical element, the light receiving element including multiple light receiving pixels arranged in a first direction at different positions on a plane perpendicular to the optical axis; wherein the multiple light receiving pixels are further arranged in a second direction intersecting the first direction to form a pixel array; characterized in that the light deflector satisfies the mathematical expressions below: 2 tan − 1 d 2 f r < θ t ≤ 2 tan − 1 Nd + N − 1 p 2 f r − 8 A sin L c ω s when N is an even number equal to 2m where m is a natural number; and 2 tan − 1 d + 2 p 2 f r < θ t ≤ 2 tan − 1 Nd + N − 1 p 2 f r − 8 A L c ω s when N is an odd number equal to 2m + 1 where m is a natural number where ω s is a sinusoidal angular velocity of scanning, A is a maximum mechanical deflection angle, L is a maximum detection distance, f r is a focal length of the light receiving optical element, d is a width of each of the light receiving pixels in the first direction, p is a distance in the first direction between adjacent light receiving pixels, c is the speed of light, θ t is a spread angle of projecting light, and N is the number of pixel arrays arranged along a direction in which horizontal shift occurs in the light receiving element due to an angle change of the light deflector. ω s is a sinusoidal angular velocity of scanning, A is a maximum mechanical deflection angle, L is a maximum detection distance, f r is a focal length of the light receiving optical element, d is a width of each of the light receiving pixels in the first direction, p is a distance in the first direction between adjacent light receiving pixels, c is the speed of light, θ t is a spread angle of projecting light, and N is the number of pixel arrays arranged along a direction in which horizontal shift occurs in the light receiving element due to an angle change of the light deflector.