A light source device comprising: a first laser diode; a second laser diode; a reflector having: a first reflecting face configured to reflect a portion of light from the first laser diode and to transmit a portion of the light from the first laser diode, a second reflecting face configured to reflect a portion of light from the second laser diode and to transmit a portion of the light from the second laser diode, a first exit face configured to allow the portion of the light transmitted through the first reflecting face to exit, and a second exit face configured to allow the portion of the light transmitted through the second reflecting face to exit; a photodetector comprising: a first light receiving element configured to receive first light exiting the first exit face, and a second light receiving element configured to receive second light exiting the second exit face; and a base directly or indirectly supporting the first laser diode, the second laser diode, the reflector, and the photodetector; wherein the reflector is configured such that the light transmitted through the first reflecting face is hindered from exiting the second exit face and the light transmitted through the second reflecting face is hindered from exiting the first exit face by configuring the reflector such that: the reflector comprises a first light shielding part (43, 43a) located between a first part defined by the first reflecting face and the first exit face, and a second part defined by the second reflecting face and the second exit face, and the first light shielding part (43, 43a) comprises either a slit-shaped groove formed in the reflector and located between the first part and the second part or a recess formed in the reflector and located in at least one of an upper face of the reflector, a lower face of the reflector, the first reflecting face, the second reflecting face, the first exit face, and/or the second exit face of the reflector. a first laser diode; a second laser diode; a reflector having: a first reflecting face configured to reflect a portion of light from the first laser diode and to transmit a portion of the light from the first laser diode, a second reflecting face configured to reflect a portion of light from the second laser diode and to transmit a portion of the light from the second laser diode, a first exit face configured to allow the portion of the light transmitted through the first reflecting face to exit, and a second exit face configured to allow the portion of the light transmitted through the second reflecting face to exit; a first reflecting face configured to reflect a portion of light from the first laser diode and to transmit a portion of the light from the first laser diode, a second reflecting face configured to reflect a portion of light from the second laser diode and to transmit a portion of the light from the second laser diode, a first exit face configured to allow the portion of the light transmitted through the first reflecting face to exit, and a second exit face configured to allow the portion of the light transmitted through the second reflecting face to exit; a photodetector comprising: a first light receiving element configured to receive first light exiting the first exit face, and a second light receiving element configured to receive second light exiting the second exit face; and a first light receiving element configured to receive first light exiting the first exit face, and a second light receiving element configured to receive second light exiting the second exit face; and a base directly or indirectly supporting the first laser diode, the second laser diode, the reflector, and the photodetector; wherein the reflector is configured such that the light transmitted through the first reflecting face is hindered from exiting the second exit face and the light transmitted through the second reflecting face is hindered from exiting the first exit face by configuring the reflector such that: the reflector comprises a first light shielding part (43, 43a) located between a first part defined by the first reflecting face and the first exit face, and a second part defined by the second reflecting face and the second exit face, and the first light shielding part (43, 43a) comprises either a slit-shaped groove formed in the reflector and located between the first part and the second part or a recess formed in the reflector and located in at least one of an upper face of the reflector, a lower face of the reflector, the first reflecting face, the second reflecting face, the first exit face, and/or the second exit face of the reflector. the reflector comprises a first light shielding part (43, 43a) located between a first part defined by the first reflecting face and the first exit face, and a second part defined by the second reflecting face and the second exit face, and the first light shielding part (43, 43a) comprises either a slit-shaped groove formed in the reflector and located between the first part and the second part or a recess formed in the reflector and located in at least one of an upper face of the reflector, a lower face of the reflector, the first reflecting face, the second reflecting face, the first exit face, and/or the second exit face of the reflector.