A rotational speed detection device, comprising: a rotating object ; a light emitting unit for emitting laser light to the rotating object ; a light receiving unit for receiving light reflected by the rotating object after being emitted from the light emitting unit to the rotating object , the light having a speckle pattern; a received light data obtaining unit for obtaining received light data of the light received by the light receiving unit ; and a rotational speed calculation unit for calculating a rotational speed of the rotating object based on the received light data received by the received light data obtaining unit , wherein the rotating object is placed in a container of a transparent or translucent material capable of transmitting light, has a spherical shape having a radius of curvature smaller than the radius of curvature of a bottom inner surface of the container , is formed from a metal conductive material and has a rotating surface, and an irregular uneven portion on the rotating surface, the received light data obtaining unit is configured to obtain time-series data of received light data of light reflected by the uneven portion , wherein received light intensity in the time-series data varies periodically to draw the same waveform each time the rotating object rotates one revolution, and the rotational speed calculation unit is configured to calculate the rotational speed of the rotating object from periodicity of the time-series data, characterised in that the uneven portion having projections and depressions; and the light emitting unit is positioned so that an optical axis of the laser light substantially coincides with a rotation axis (CL) of the rotating object , and is configured to emit the laser light to a circular region having a center at the rotation axis (CL),the light receiving unit is positioned to face a curved surface of a lower portion of the rotating object which is illuminated with the laser light. a rotating object ; a light emitting unit for emitting laser light to the rotating object ; a light receiving unit for receiving light reflected by the rotating object after being emitted from the light emitting unit to the rotating object , the light having a speckle pattern; a received light data obtaining unit for obtaining received light data of the light received by the light receiving unit ; and a rotational speed calculation unit for calculating a rotational speed of the rotating object based on the received light data received by the received light data obtaining unit , wherein the rotating object is placed in a container of a transparent or translucent material capable of transmitting light, has a spherical shape having a radius of curvature smaller than the radius of curvature of a bottom inner surface of the container , is formed from a metal conductive material and has a rotating surface, and an irregular uneven portion on the rotating surface, the received light data obtaining unit is configured to obtain time-series data of received light data of light reflected by the uneven portion , wherein received light intensity in the time-series data varies periodically to draw the same waveform each time the rotating object rotates one revolution, and the rotational speed calculation unit is configured to calculate the rotational speed of the rotating object from periodicity of the time-series data, characterised in that the uneven portion having projections and depressions; and the light emitting unit is positioned so that an optical axis of the laser light substantially coincides with a rotation axis (CL) of the rotating object , and is configured to emit the laser light to a circular region having a center at the rotation axis (CL),the light receiving unit is positioned to face a curved surface of a lower portion of the rotating object which is illuminated with the laser light. <EOS>