A laser apparatus is provided which is capable of achieving deep penetration into an aluminum-like metal material without causing welding defects such as spatters or cracks and performing high-speed pulse seam welding. The laser apparatus includes a pulse power source that generates a current signal and a mask signal for masking a fluctuation component included in the current signal, and which supplies a current signal in which a fluctuation component has been masked by the mask signal to a YAG pulsed laser oscillator. In addition, the laser apparatus sets the spot shape of a CW laser light oscillated by a CW laser oscillator to a rhombic streamlined shape, and causes a focus spot of the CW laser light to include a circular focus spot of a pulsed laser light.