A laser device for irradiating an object to be irradiated, with laser light, the laser device comprising: a laser source configured to emit the laser light; an optical system configured to irradiate the object with the laser light emitted from the laser source, and capable of changing a beam profile of the laser light projected on the object; a profile detection unit configured to detect the beam profile of the laser light emitted from the optical system to the object; and a control unit configured to perform control processing for controlling the optical system so that the beam profile detected by the profile detection unit is a desired beam profile in each predetermined control cycle, a control cycle being a cycle of executing the control processing, wherein, the object is an optical fiber including a first core and a second core surrounding the first core, the laser light emitted from the optical system is configured to be projected onto the end of the optical fiber, the beam profile detected by the profile detection unit includes a position of a spot of the laser light at the end of the optical fiber, the control unit is configured to control the optical system so that the position of the spot detected by the profile detection unit is a target spot position according to the desired beam profile, the profile detection unit includes a partial reflection mirror configured to reflect a part of the laser light traveling from the optical system toward the end of the optical fiber, and a partial light receiver configured to receive the part of the laser light reflected by the partial reflection mirror and configured to then output an electrical signal corresponding to the conditions of receiving the partial light (LBa) and to transmit the output to the control unit, and characterized in that: the control unit is configured to set the control cycle to: a first cycle, if the target spot position is set at a boundary between the first core and the second core of the optical fiber, the first cycle being short with respect to a second cycle to increase the frequency of executing the control processing by the control unit; and the second cycle longer than the first cycle, if the target spot position is not set at the boundary to decrease the frequency of executing the control processing by the control unit. a laser source configured to emit the laser light; an optical system configured to irradiate the object with the laser light emitted from the laser source, and capable of changing a beam profile of the laser light projected on the object; a profile detection unit configured to detect the beam profile of the laser light emitted from the optical system to the object; and a control unit configured to perform control processing for controlling the optical system so that the beam profile detected by the profile detection unit is a desired beam profile in each predetermined control cycle, a control cycle being a cycle of executing the control processing, wherein, the object is an optical fiber including a first core and a second core surrounding the first core, the laser light emitted from the optical system is configured to be projected onto the end of the optical fiber, the beam profile detected by the profile detection unit includes a position of a spot of the laser light at the end of the optical fiber, the control unit is configured to control the optical system so that the position of the spot detected by the profile detection unit is a target spot position according to the desired beam profile, the profile detection unit includes a partial reflection mirror configured to reflect a part of the laser light traveling from the optical system toward the end of the optical fiber, and a partial light receiver configured to receive the part of the laser light reflected by the partial reflection mirror and configured to then output an electrical signal corresponding to the conditions of receiving the partial light (LBa) and to transmit the output to the control unit, and characterized in that: a partial reflection mirror configured to reflect a part of the laser light traveling from the optical system toward the end of the optical fiber, and a partial light receiver configured to receive the part of the laser light reflected by the partial reflection mirror and configured to then output an electrical signal corresponding to the conditions of receiving the partial light (LBa) and to transmit the output to the control unit, and characterized in that: the control unit is configured to set the control cycle to: a first cycle, if the target spot position is set at a boundary between the first core and the second core of the optical fiber, the first cycle being short with respect to a second cycle to increase the frequency of executing the control processing by the control unit; and the second cycle longer than the first cycle, if the target spot position is not set at the boundary to decrease the frequency of executing the control processing by the control unit. a first cycle, if the target spot position is set at a boundary between the first core and the second core of the optical fiber, the first cycle being short with respect to a second cycle to increase the frequency of executing the control processing by the control unit; and the second cycle longer than the first cycle, if the target spot position is not set at the boundary to decrease the frequency of executing the control processing by the control unit.