An optical apparatus configured to perform one or both of writing and erasing of information with respect to a reversible recording medium including a plurality of recording portions including a reversible heat-sensitive color developing composition and a photothermal conversion agent, the reversible heat-sensitive color developing composition varying in developed-color tone for each of the recording portions, and the photothermal conversion agent varying in absorption wavelength for each of the recording portions in a near infrared region (700 nm to 2500 nm), the optical apparatus comprising: a plurality of laser devices (31A, 31B, 31C) configured to vary in emission wavelength in a near infrared region; an optical system configured to multiplex laser beams outputted from the plurality of laser devices; a scanner unit configured to scan a multiplexed light beam obtained by multiplexing by the optical system, on the reversible recording medium, wherein the laser devices each are configured to output a laser beam under a condition that a temperature of the recording portion to be subjected to writing is set to be a color developing temperature or higher due to heat generation by the photothermal conversion agent, when performing writing with respect to the reversible recording medium, and wherein the laser devices each are configured to output a laser beam under a condition that a temperature of the recording portion to be subjected to erasing is set to be a temperature that is a discoloring temperature or higher and is lower than a color developing temperature due to heat generation by the photothermal conversion agent, when performing erasing of information written in the reversible recording medium; and characterized by further comprising a control (10, 20) mechanism that is configured to control the energy density [W/cm 2] on the reversible recording medium to have an energy density [W/cm 2] on the reversible recording medium when erasing information written in the reversible recording medium is performed which energy density is smaller than the energy density [W/cm 2] on the reversible recording medium when writing in the reversible recording medium is performed. a plurality of laser devices (31A, 31B, 31C) configured to vary in emission wavelength in a near infrared region; an optical system configured to multiplex laser beams outputted from the plurality of laser devices; a scanner unit configured to scan a multiplexed light beam obtained by multiplexing by the optical system, on the reversible recording medium, wherein the laser devices each are configured to output a laser beam under a condition that a temperature of the recording portion to be subjected to writing is set to be a color developing temperature or higher due to heat generation by the photothermal conversion agent, when performing writing with respect to the reversible recording medium, and wherein the laser devices each are configured to output a laser beam under a condition that a temperature of the recording portion to be subjected to erasing is set to be a temperature that is a discoloring temperature or higher and is lower than a color developing temperature due to heat generation by the photothermal conversion agent, when performing erasing of information written in the reversible recording medium; and characterized by further comprising a control (10, 20) mechanism that is configured to control the energy density [W/cm 2] on the reversible recording medium to have an energy density [W/cm 2] on the reversible recording medium when erasing information written in the reversible recording medium is performed which energy density is smaller than the energy density [W/cm 2] on the reversible recording medium when writing in the reversible recording medium is performed.