There is provided a microchip that is formed of a first substrate having a surface with a groove and a second substrate joined together and has a fluid circuit in the form of a cavity defined by the groove and a surface of the second substrate closer to the first substrate. The fluid circuit at least includes a detection portion having an optical path for transmitting light. The microchip includes at least one of a step defined by a groove formed in contact with at least one side surface of a groove of the first substrate that defines the optical path and a recess provided in the second substrate at a position opposite to the step.