To provide optical modules and optical transmission devices that are suitable for communication forms using multimode optical fibers, an optical module includes a surface-emitting type semiconductor laser that emits polarized light oscillating in a multimode which is preferentially oriented in two given polarization axes, and an optical member that demonstrates at least one function among a transmission function, a reflection function, a refraction function, and a diffraction function alternatively to a predetermined polarization. The optical member is disposed such that a principal plane thereof intersects with a traveling direction of emission light of the surface-emitting type semiconductor laser and a polarization axis of the polarization plane does not overlap with the polarization axes of the emission light of the surface-emitting type semiconductor laser.